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chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Contents lists available at ScienceDirect

Chemical Engineering Research and Design

journa l homepage: www.e lsev ier .com/ locate /cherd

dsorption and visible-light photocatalyticegradation of tetracycline hydrochloride fromqueous solutions using 3D hierarchicalesoporous BiOI: Synthesis and characterization,

rocess optimization, adsorption and degradationodeling

liakbar Dehghanb,∗, Mohammad Hadi Dehghania,b,c,∗∗,amin Nabizadehb, Navid Ramezaniand,ahmood Alimohammadib, Ali Asghar Najafpoore

Center for Water Quality Research, Institute for Environmental Research, Tehran University of Medical Sciences,ehran, Islamic Republic of IranDepartment of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences,ehran, Islamic Republic of IranCenter for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences,ehran, Islamic Republic of IranDepartment of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of IranDepartment of Environmental Health Engineering, School of Health, Social Determinants of Health Researchentre, Mashhad University of Medical Sciences, Mashhad, Islamic Republic of Iran

r t i c l e i n f o

rticle history:

eceived 18 June 2017

eceived in revised form 25

eptember 2017

ccepted 2 November 2017

vailable online 11 November 2017

eywords:

dsorption

inetic and isotherm

isible-light photocatalytic

D hierarchical mesoporous BiOI

a b s t r a c t

Presence of antibiotics in aquatic environment has raised public concerns due to poten-

tial adverse effects. In this study, we synthesized two different bismuth oxyiodide (BiOI)

by hydrolysis (BiOI-H) and solvothermal (BiOI-ST) methods and characterized using FTIR,

XRD, FESEM, N2 adsorption–desorption isotherm, DRS and PLS. The results of characteri-

zation tests showed that the BiOI-ST sample is a better adsorbent and may be more active

in photocatalytic reactions as the result of more surface area, higher light absorption abil-

ity lower band-gap energy and PL intensity, than BiOI-H. Tetracycline hydrochloride (TCH)

antibiotic was selected to evaluate adsorption and photocatalytic efficiency of BiOI-ST using

Response Surface Methodology. The optimum conditions of contact time, TCH initial con-

centration, BiOI dosage and pH for adsorption and photocatalytic processes were obtained

37.5 min, 2.1 mg/L, 1.5 g/L, 8.5 and 101.5 min, 2 mg/L, 0.68 g/L, respectively. Based on kinetic

and isotherm studies, experimental data fitted to pseudo-second order kinetics model and

followed the Freundlich and D–R isotherm models. The apparent pseudo-first order rate

constant of BiOI-ST was higher than that of BiOI-H. Therefore, BiOI-ST can be used as a

promising option to treat

© 2017 Institution of C

∗ Corresponding author.∗∗ Corresponding author at: Center for Water Quality Research, Institute foehran, Islamic Republic of Iran.

E-mail addresses: aliakbardehghan@gmail.com (A. Dehghan), hdeabizadeh), ramezanian@um.ac.ir (N. Ramezanian), m alimohammadajafpoor).ttps://doi.org/10.1016/j.cherd.2017.11.003263-8762/© 2017 Institution of Chemical Engineers. Published by Elsev

low level concentration of TCH in hospital wastewaters.

hemical Engineers. Published by Elsevier B.V. All rights reserved.

r Environmental Research, Tehran University of Medical Sciences,

hghani@tums.ac.ir (M.H. Dehghani), rnabizadeh@tums.ac.ir (R.i@tums.ac.ir (M. Alimohammadi), najafpooraa@mums.ac.ir (A.A.

ier B.V. All rights reserved.

218 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Fig. 1 – a) TCH molecular structure and b) its pH-dependentspeciation.

1. Introduction

In the recent years, the presence of antibiotics in aquatic environ-

ment such as rivers, streams, lakes and groundwater has raised public

concerns due to potential adverse effects (Zhang et al., 2015). Most of

antibiotics are excreted through treated human and animals’ urine and

feces as unchanged compounds because of poor metabolization and

absorption (Oladoja et al., 2014); especially, tetracycline hydrochloride,

the second most produced and used antibiotic, that may lead to dis-

rupting soil respiration, Fe(III) reduction, nitrification and phosphatase

activities (Gao et al., 2012). Thus, it is necessary to research on new

efficient treatment technologies to remove these antibiotics from envi-

ronment. Today, many technologies have been reported for removal

of tetracycline antibiotics including membrane (Koyuncu et al., 2008),

adsorption (Gao et al., 2012), coagulation (Jia et al., 2016), electrochem-

ical process (Oturan et al., 2013) and photocatalytic degradation (Zhu

et al., 2013). Among these available methods, adsorption and photocat-

alytic degradation have been widely used to remove many pollutants

(Dehghani et al., 2015, 2016a,b, 2017a; Oskoei et al., 2016) including

tetracycline (Zhang et al., 2015; Zhu et al., 2013; Yu et al., 2014; Acosta

et al., 2016) from aqueous environments. Due to simplicity and high

efficiency, adsorption has always been an effective method for removal

of tetracycline (Zhang et al., 2015).

In addition, advanced oxidation processes (AOPs) such as hetero-

geneous photocatalysis have attracted more attention in elimination

of high recalcitrant and nonbiodegradable pollutants because of their

high efficiency, complete pollutants mineralization to CO2, simplicity

of operation and low cost (Xiao et al., 2015). Among materials used

as photocatalyst, TiO2 with high chemical stability, efficient photo-

catalytic degradation and nontoxicity is a promising photocatalyst to

degrade and mineralize pollutants in water and wastewater matrices

(Xiao et al., 2015). However, TiO2 is not effective under ultraviolet spec-

trum (<400 nm), which is related to the large band gap of photocatalyst

(Yu et al., 2014). As a result, synthesis and development of new photo-

catalyst materials with strong absorbance in visible light region have

great importance. Recently, a novel family of photocatalyst, bismuth

oxyhalides (BiOX, X = Cl, Br and I), have attracted considerable atten-

tion because of their uniquely layered structure features, which can

induce the effective separation of photogenerated electron–hole pairs

(Xiao et al., 2012; Weng et al., 2014). Among various bismuth oxyhalides,

BiOI has the smallest band gap and higher photocatalytic activity than

BiOCl and BiOBr. Many scientists have reported that BiOI-based pho-

tocatalysts can effectively decompose pollutants such as dyes (Weng

et al., 2014; Li et al., 2011; Ge et al., 2012), antibiotics (Yu et al., 2014),

phenolic compounds (Li et al., 2011; Han et al., 2015; Pan et al., 2015)

under visible-light irradiation. However, only a few studies have been

conducted to the adsorption properties of BiO. Zhang et al. (2013) inves-

tigated the adsorption of RhB dye on different BiOX and reported that

BiOI can efficiently remove RhB dye from aqueous solution. It is of great

importance to note that the main disadvantage of these studies is lack

of optimization of influential variables including pH solution, pollu-

tant initial concentration, catalyst dosage and reaction time on removal

efficiency of BiOI-based photocatalysts.

Optimization of variables in classic method is carried out through

varying one parameter at a time keeping the others constant, which is

laborious, time consuming and disable to predict the combined effects

of independent variables on response at a time (Dehghani et al., 2017b).

Statistical experimental design with RSM is a good technique to over-

come such drawbacks in which the combined effects of factors involved

in optimization process are investigated (Dehghani et al., 2017b). So far,

no study has been reported on the optimization of adsorption and pho-

tocatalytic process of BiOI-based photocatalysts and to the best of our

knowledge, this is the first report on RSM optimization.

The main aims of this study were to synthesis and characterize the

bismuth oxyiodide photocatalyst by two kinds of methods, optimizing

its efficiency and investigating the effects of process variables including

reaction time, BiOI dosage, pH solution and TCH initial concentra-

tion on removal percentage as response by RSM using adsorption and

photocatalytic degradation processes. Adsorption kinetic and isotherm

studies as well as degradation kinetic were implemented in this study.

2. Experimental

2.1. Chemicals

All chemicals used in this study were of analytical grade andused without further purification. Nitrate bismuth (Bi(NO3)3,5H2O) were purchased from Sigma–Aldrich, whereas potas-sium iodide (KI) was from Merck. Tetracycline hydrochloride(TCH) was prepared from a pharmaceutical company inTehran, Iran. Molecular structure and pH-dependent specia-tion of TCH are depicted in Fig. 1.

2.2. Synthesis of BiOI

In a typical synthesis, two common methods were used toprepare BiOI samples. In solvothermal BiOI (BiOI-ST), 1.51 gBi(NO3)3, 5H2O was dissolved in 10 mL ethylene glycol by stir-ring for 45 min to form solution A; 0.5 g KI was added into 5 mLHPLC grade distillated water to form solution B. In continua-tion, solution B was added dropwise using medical syringeto solution A under magnetic stirring. The obtained mixturewas stirred for 2 h at room temperature. After that, the formedsolution was transferred into a 100 mL Teflon-lined stainlessautoclave and kept at temperature 180 ◦C for 12 h. After cool-ing, the solution was filtrated and washed several time withdouble distillated water and absolute ethanol. Then, the resul-tant precipitate was dried at 60 ◦C for 6 h. on the other hand, toperform a comparative study, hydrolysis BiOI (BiOI-H) samplewas also prepared similar to solvothermal method with twodifferences: (1) magnetic stirring of A and B mixture for 5 hand (2) omitting thermal treatment step.

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 219

2

TorodmastAaaTsdwLimw

2

AEhrAswRTtsd

2

Ptlctasst

2

Im

.3. Characterization of BiOI

he Fourier transform infrared spectra (FTIR) was recordedn Thermo Nicolet, Avatar 370 model FTIR using KBr as aeference material in the range of 400–4000 cm−1 with a res-lution of 4 cm−1 and 16 scans. Crystalline phase of BiOI wasetermined by X-ray diffractometer (Unisantis S.A, XMD300odel, Geneva, Switzerland) With Cu-K� as source radiation

t wavelength 0.154 nm. The surface morphology of preparedamples was characterized by field emission scanning elec-ron microscopy (FE-SEM, MIRA3 TESCAN, Czech Republic).ccording to the Brunauer–Emmett–Teller analysis, nitrogendsorption isotherm was used to measure specific surfacerea using surface area and porosity analyzer (Micromeritics,riStar II Plus, USA), and the pore size distribution was mea-ured by the Barrett–Joyner–Halenda (BJH) method based onesorption isotherm. UV–vis diffuse reflectance spectra (DRS)ere measured on a UV–vis spectrophotometer (PerkinElmer,

ambda 950, USA) by using BaSO4 as a reference material. Var-an Cary Eclipse Fluorescence Spectrophotometer was used to

easure the photoluminescence (PL) spectra of BiOI samplesith Xenon lamp as excitation source at wavelength 265 nm.

.4. Adsorption test

dsorption experiments were performed in 250 mL glassrlen-meyer flask containing 100 mL of tetracyclineydrochloride solutions. All the experiments were car-ied out in dark environment at room temperature (25 ± 2 ◦C).

given amount of adsorbent was added to 100 mL TCHolutions with the specified concentration and pH. Then,orking solutions were transferred to magnetic stirrer (IKA

®,

O 10 p model, Staufen, Germany) and agitated at 100 rpm.hence, 2.5 mL solution was taken out at the predetermined

ime intervals and filtrated by 0.22 �m cellulose acetateyringe membrane filter. The filtration solution was used foretermining TCH concentration.

.5. Photocatalytic activity test

hotocatalytic activity of BiOI sample was examined in pho-ochemical reactor equipped with a 1000 W tungsten halogenamp (ORSAM GmbH, Germany) as light source and 420 nmutoff filter by degradation of TCH under visible light irradia-ion. The light source was placed in cylindrical glass cold trapnd a water circulation system established to cool reactionystem. Before to light illumination for each experiment, theuspension of TCH and catalyst was magnetically stirred inhe dark for 1 h to ensure adsorption–desorption equilibrium.

.6. TCH analysis

n all of experiments, the concentration of TCH was deter-ined by a high liquid performance chromatography (HPLC,

Table 1 – Experimental level of the independent variables in ad

Factors Coded variables (Xi)

Adsorp

−1 −

Contact time (min) X1 5.0 18.75

Adsorbent dosage (g L–1) X2 0.1 0.575

Solution pH X3 1.0 2.0

TCH concentration (mg L–1) X4 3.0 5.0

Smartline, Knauer, Germany) equipped with a separation col-umn C18 (5 �m, 4.6 �m × 150 mm) using Ultraviolet detector ata wavelength of 261 nm. A mixture of mobile phases includ-ing acetonitrile and HCl solution 0.01 M in a ratio of 20, 80 (v/v)was injected into HPLC at the flow rate 0.8 mL min−1.

2.7. Central composite design (CCD)

Experimental design optimizes the effect of different variablesand their interactions in a process which result in improvingthe performance of parameters and decreasing the inaccu-racy of experiments (Dehghani et al., 2017b). Response SurfaceMethodology is a technique that combines statistical andmathematical methods to model and optimize the influen-tial variables on response factor. Central composite design, amost commonly used sub-section under RSM, has three mainsteps including experimental design, modeling, and optimiza-tion (Asfaram et al., 2015). In this study, a CCD with five-levelwas designed to optimize independent variables. Individualvariables and their levels are given in Table 1 for each process.Finally, two CCD consist of 44 and 22 runs was suggested byR3.0.2 software (Stat Soft Inc., Tulsa, USA) for adsorption andphotocatalytic processes, respectively.

After performing designed experiments, the results ofresponse were optimized by quadratic model as follow:

y = b0 + �4i=1bixi + �4

i=1�4j=1bijxixj + �4

i=1biix2i (1)

where y is the response variable (TCH removal, %), xi and xjare the independent variables, b0 is the model constant; bi isthe linear coefficient, bii is the quadratic coefficient, and bij isthe interaction coefficient.

3. Results and discussion

3.1. BiOI characterization

XRD, FESEM, FTIR, N2 adsorption–desorption isotherm, DRSand PLS were applied to characterize the prepared BiOI sam-ples. The FTIR spectrums of BiOI samples before and afterTCH adsorption are shown in Fig. 2. The major absorptionbands of BiOI-H at 3460.58, 1612.63, 1495.12, 1383.73, 1262.2,739.16, 485.61 cm−1 shifted to 3426.62, 1627.8, 1301.73, 1073.51,769.87, 562.66, 449.93 cm−1 in BiOI-ST. On the other hand,the observed peak of BiOI-H at 2917.14 cm−1 was disappearedin the FTIR spectrum of BiOI-ST. Absorption bands in rangeof 400–700 cm−1 can be ascribed to stretching vibrations ofBi O, Bi O I and Bi O Bi in bismuth oxyiodide (Lin et al.,2014; Lee et al., 2015). Stretching vibrations of Bi O in BiOI-H and BiOI-ST was found at the characteristic peaks 485.61and 449.93 cm−1, respectively. The characteristic peaks of BiOI

samples at 3460.58, 1612.63 cm−1 and 3426.62, 1627.8 cm−1 isprobably attributed to the adsorption of water or hydroxyl

sorption and photocatalytic processes.

Variable levels

tion process Photocatalytic process

0 + 1 −1 −˛ 0 + 1

32.5 46.25 60 15.0 36.28 67.5 98.71 1201.05 1.525 2.0 0.1 0.28 0.55 0.81 13.0 4.0 5.07.0 9.0 11.0 1.0 1.81 3.0 4.18 5

220 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Fig. 2 – FTIR spectra of (a) BiOI-H, (b) BiOI-ST and (c) BiOI-STafter adsorption of TCH.

Fig. 3 – XRD pattern of (a) BiOI-H and (b) BiOI-ST.

activity of catalysts (Xiao et al., 2012). Higher photocatalytic

groups (Mehraj et al., 2016). The peak recognized at 1383.73and 1301.73 can be assigned to adsorption of OH groups onhydrogen related defects (Vinoth et al., 2017). The observedpeak at 1462 cm−1 is related to the �(C O), demonstratingvery weak characteristic peaks of CO3

−2 (Lee et al., 2015).About BiOI-ST, after TCH adsorption, not only peak inten-sities decreased but also new peaks were found at 1781.16,1454.26, 1221.34 and 407.37 cm−1 absorption bands, implyingthat adsorbing TCH on BiOI-ST has been occurred.

Fig. 3 shows XRD pattern of BiOI samples. One can see thatBiOI crystal planes of (002), (012), (110), (004), (020) and (212)are corresponding to 2� values at 19.5, 29.7, 32.7, 39.3, 45.4 and55.2, respectively (Jamil et al., 2015). These crystal planes werealso manifested in two prepared BiOI samples. The sharp andstrong peaks indicate that the as prepared BiOI samples havehigh crystallinity (Mehraj et al., 2016). The more intensity andmore sharp peaks, the more crystalline structure and morecrystal size would be (Jamil et al., 2015). In the case of BiOI-H,the sharp peaks with higher intensity obtained while BiOI-STsample had wider peaks with lower intensity, which imply thatthe reaction temperature play a key role in reducing the crys-

tallinity of BiOI-ST. The diffraction peaks in prepared samples

are well matched with those reported by other researchers forBiOI (Ge et al., 2012).

To estimate average crystallite size of BiOI samples, X-raydiffraction peaks (012) was used based on Scherer formula(Jamil et al., 2015):

D = K�

ˇcos�(2)

where D is the crystallite size, � is the wavelength of X-rayradiation (� = 0.15418 nm), K is the Scherer constant (K = 0.94),� is the angle of x-ray diffraction and is full width ofhalf maximum (FWHM) of the (012) plane. With respect toEq. (2), the crystallite size of BiOI-H and BiOI-ST is about24.25 and 40.42 nm, respectively. The particle size plays animportant role in determining adsorption and photocatalyticdegradation properties of semiconductors (Xiao et al., 2012).Photocatalytic activity of semiconductor would increase withsmaller particle size because of available larger surface area(Xiao et al., 2012). Recent studies have shown that sharpdiffraction peaks and higher peak intensity of semiconductorreveal its larger crystal size (Jamil et al., 2015). In this study,in spite of sharp diffraction peaks with higher intensity inthe XRD pattern of BiOI-H sample, smaller particle size wasobserved for it.

The FESEM image of BiOI demonstrated that the morphol-ogy of BiOI-H was constituted by the irregular nanoplates,which were tightly connected to each other (Fig. 4a and b).But in BiOI-ST, this morphology was changed to 3D hierar-chical structure with very regular thin-nanosheets because ofthermal treatment step (Fig. 4c and d). As it can be seen inFig. 4e and f, adsorbing TCH on BiOI-ST nanosheets has causedchanges in surface properties and thickness of nanosheets.

Fig. 5 shows N2 adsorption–desorption isotherm and porediameter distribution for BiOI samples. As it is clear, both ofthe two prepared samples exhibit isotherm type IV with a H3hysteresis loop in the relative pressure range between 0.5–0.95,implying the presence of mesoporous structure. The surfacearea of BiOI-H and BiOI-ST based on BET isotherm (ABET) was of8.0034 and 26.659 m2 g−1, respectively. Barrett–Joyner–Halendamethod was used to calculate the pore size distribution curveof BiOI samples (inset in Fig. 5a, b). Pore volume and meanpore diameter were 0.0141 cm3 g−1, 1.2 nm for BiOI-H and0.0411 cm3 g−1, 1.2 nm for BiOI-ST. Mesoporous structure ofsamples could be attributed to the interaggregation of BiOIsheets in the microparticles (Li et al., 2011).

The UV–vis diffuse reflectance of BiOI samples is presentedin Fig. 6. As shown in Fig. 6, both the as-prepared samplesexhibit absorption at range 300–650 nm but the BiOI-H showbetter photoabsorption, while the photoabsorption of BiOI-STeven extend beyond the visible light region. Optical absorptionedges were obtained as 675 and 785 nm for BiOI-H and BiOI-ST,respectively. The energy band gap of indirect semiconductorcan be calculated from the equation below (Senthilnathan andPhilip, 2010; Chen et al., 2015):

Eg = 1239.8�

(3)

Here, Eg (eV) is the band gap and � is the wavelength of opti-cal adsorption edge (nm). According to this, the band gap ofBiOI samples was 1.836 eV for BiOI-H and 1.579 eV for BiOI-ST.Band-gap energy is a key factor to determine photocatalytic

ability is attributed to the smaller band-gap energy owing to

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 221

T (c,

t(wa

cpTrLep

Fig. 4 – FESEM images of BiOI-H (a, b), BiOI-S

he lower energy required to stimulate photocatalytic reactionXiao et al., 2012). In this study, the band-gap energy of BiOI-STas smaller than that of BiOI-H and those reported by other

uthors (Ge et al., 2012; Han et al., 2015; Pan et al., 2015).Besides the particle size, photocatalytic activity of semi-

onductor is dependent on the recombination rate ofhotoinduced electrons and holes pair (He et al., 2015).o explore separation capacity of photogenerated car-iers, PL spectra was employed as shown in Fig. 7.ower photoluminescence intensity is indicative of reducedlectron–hole recombination rate and higher activity in

hotocatalytic reactions (Zhang, 2014; Liu et al., 2013).

d) and BiOI-ST after adsorption of TCH (e, f).

As can be seen in Fig. 7, PL spectra of BiOI samplesshow two distinct peaks around 360 and 425 nm, imply-ing quick recombination of most of charges in BiOI. But,intensity of peaks considerably reduced in BiOI-ST sam-ple, which is the result of this fact that electron–holerecombination is well prevented on the surface of BiOI-ST. in spite of larger crystal size, the BiOI-ST samplepropound higher photocatalytic activity than to BiOI-Hbecause of its smaller band-gap energy, higher surfacearea and lower recombination of the photoinduced chargecarriers, and thus was used to model and optimize removal

of TCH.

222 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Fig. 5 – N2 adsorption–desorption isotherm and pore sizedistribution curve of a) BiOI-ST and b) BiOI-H.

Fig. 6 – UV–vis diffuse reflectance spectrum of BiOI-H andBiOI-ST.

Fig. 7 – Photoluminescence spectra of BiOI samples.

3.2. Process optimization

To optimize the selected independent variables consist of TCHconcentration, pH, dosage and contact time, the designedexperiments suggested by CCD were performed according toTables 2 and 3. Analysis of variance (ANOVA) was employedto evaluate the effect of independent variables on response.By employing the second-order equation on the values ofresponse (TCH removal), the following reduced quadraticmodels were developed:

Adsorption process:

y = 80.229 + 6.7483X1 + 19.36X2 + 19.2383X3 − 16.5417X4

−15.27X2X3 + 3.5527X21 − 4.0423X2

2 − 16.4923X23

+3.7877X24 (4)

Photocatalytic process:

y = 69.3305 + 24.3459X1+9.2074X2−19.4139X3−2.0153X1X3

+4.9851X2X3+4.7494X21 − 14.8006X2

2 + 7.4994X23 (5)

The ANOVA results of response values are shown in Table 4.Based on ANOVA, in adsorption process, the linear effect ofprocess variables, the interaction effect of adsorbent dosageand solution pH and quadratic effect of pH were significant,while in photocatalytic process, only the quadratic effect ofcatalyst dosage associated with the linear effect of processvariables were significant. The P-value, R2 and lack of fit wereused to judge on the accuracy of the model (Dehghani et al.,2017c), so that the higher values of p-value and R2 and insignif-icance of lack of fit show that the model has high abilityto correlate experimental and predicted values of response(Dehghani et al., 2017c).

According to Table 4, the coefficients of determination(R2) were 0.9001 and 0.9142 for adsorption and photocatalyticprocesses, respectively, which means that the independentvariable is responsible for 90% and 91.42% of the variation.Besides, the adjusted R2 values of 0.8737 and 0.8614 for mod-els are as high as close to R2 values. The normal distributionof the experimental data is an important factor in statisti-cal analysis (Asfaram et al., 2016). Residual was applied tojudge the normality of the experimental data, which describesthe difference between experimental and predicted values. Byplotting the residuals against these deviations, it was foundthat the data points fall nearly along a straight line for bothprocesses. The high values of R2, the insignificant value of lackof fit (0.18692 for adsorption and 0.07199 for photocatalyticprocess) and significant P-value of each model confirmed thestatistically adequacy of the models.

The most influential model terms in TCH adsorption were,in order: adsorbent dosage (X2), pH (X3), initial TCH concentra-tion (X4) and contact time (X1). In contrary, the contact time(X1) had the highest effect on photocatalytic degradation ofTCH, initial TCH concentration (X4) and catalyst dosage (X2)were the next ranks.

Assessment of optimum conditions of TCH removal wasperformed by a solver program in Microsoft Office Excel2007 software. To obtain maximum TCH removal (100%),we selected the independent variables in the studied range.

According to the program, the optimum conditions to get max-imum TCH removal are able to achieve by contacting 2.1 mg/L

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 223

Table 2 – The designed experiment and values of response for TCH adsorption.

Run.order Std.order Time (min, X1) Dose (g/L, X2) Concentration (mg/L, X3) pH (X4) Removal %

Experimental Predicted

1 5 46.25 0.575 2 5 69.00 65.462 21 32.50 1.050 3 7 76.26 80.233 6 46.25 0.575 2 9 99.34 92.334 1 18.75 0.575 2 5 56.92 58.715 18 32.50 1.050 3 7 77.25 80.236 15 46.25 1.525 4 5 71.75 75.917 14 46.25 0.575 4 9 76.04 75.798 20 32.50 1.050 3 7 76.26 80.239 12 18.75 1.525 4 9 86.66 80.7710 28 32.50 1.050 3 7 77.25 80.2311 13 46.25 0.575 4 5 51.46 48.9212 9 18.75 0.575 4 5 42.76 42.1713 10 18.75 0.575 4 9 72.62 69.0414 11 18.75 1.525 4 5 67.77 69.1615 17 32.50 1.050 3 7 76.26 80.2316 26 32.50 1.050 3 7 77.25 80.2317 27 32.50 1.050 3 7 76.26 80.2318 3 18.75 1.525 2 5 87.97 85.7119 7 46.25 1.525 2 5 91.42 92.4520 23 32.50 1.050 3 7 77.25 80.2321 19 32.50 1.050 3 7 76.26 80.2322 2 18.75 0.575 2 9 91.42 85.5823 16 46.25 1.525 4 9 91.11 87.5224 8 46.25 1.525 2 9 99.34 104.0625 4 18.75 1.525 2 9 99.34 97.3126 24 32.50 1.050 3 7 77.25 80.2327 25 32.50 1.050 3 7 76.26 80.2328 22 32.50 1.050 3 7 77.25 80.231 9 32.50 1.050 3 7 85.44 80.232 10 32.50 1.050 3 7 85.44 80.233 14 32.50 1.050 3 7 85.44 80.234 8 32.50 1.050 5 7 65.28 67.485 16 32.50 1.050 3 7 85.44 80.236 15 32.50 1.050 3 7 85.44 80.237 5 5.00 1.050 3 7 71.45 77.038 12 32.50 1.050 3 7 85.44 80.239 1 32.50 1.050 3 3 47.47 44.5010 2 32.50 1.050 3 11 73.50 82.9811 7 32.50 1.050 1 7 96.25 100.012 4 32.50 2.00 3 7 96.90 95.5513 13 32.50 1.050 3 7 85.44 80.2314 6 60.00 1.050 3 7 89.61 90.5315 11 32.50 1.050 3 7 85.44 80.23

3

T3ct

3

FSie3cpocorXo

16 3 32.50 0.10

CH initial concentration with 1.5 g/L BiOI at pH 8.5 and time7.5 min for TCH adsorption process and 2 mg/L TCH initialoncentration with 0.68 g/L BiOI at time 101.5 min in TCH pho-ocatalytic degradation.

.3. The effects of process variables on TCH removal

ig. 8 shows the effects of independent variables on response.olution pH is one of the most important parameters affect-

ng removal efficiency of tetracyclines (Bagda et al., 2013; Chent al., 2011; Ersan et al., 2013). TCH has a three main pKa at.3, 7.7 and 9.7 (Chen et al., 2011). Therefore, solution pH canonsiderably change the surface speciation of TCH so that atH ranges <3, 3–6.5 and above 7.7, molecular conformationf TCH is positive (H2L0), neutral and negative (HL− and L2−)harged, respectively (Chen et al., 2011). Maximum adsorptionf TCs was reported to be usually in acidic and neutral pHanges (Zhang et al., 2015; Gao et al., 2012; Acosta et al., 2016;

u and Li, 2010; Ersan, 2016; Chen and Huang, 2010). But inur study, as seen in Fig. 8a, adsorption of TCH increased as

7 48.97 56.83

pH of the solution varied from 3 to 10 and maximum adsorp-tion occurred in pH 9. As a result, this adsorption behaviorof BiOI can be ascribed to the change in TCH speciation andsurface characteristics of adsorbent (Liu et al., 2012). In orderto better understand the mechanism of pH effect on TCHremoval, pHpzc of BiOI was investigated and reported to bein range of 5–6. At solution pH lower than pHpzc, the surfaceof adsorbent is positively charged and as pH increased overpHpzc the dominant surface charge on the adsorbent is nega-tive (Guler and Sarioglu, 2014). Up to pH 5, adsorption of TCHis probably related to electrostatic interaction between posi-tively surface of BiOI and more number of negatively chargedtetracycline molecules (Zhao et al., 2011). At pH between 5and 6, despite neutral surface charge density of BiOI and TCHmolecules, increasing TCH removal is due to physical adsorp-tion instead of electrostatic interactions (Acosta et al., 2016).In basic condition, the prevailing mechanism for removal iselectrostatic interaction between protonated amino group of

TCH and negative surface charge of adsorbent (Bagda et al.,

224 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Table 3 – The designed experiment and values of response for photocatalytic degradation of TCH.

Run.order Std.order Time (min, X1) Dose (g/L, X2) Concentration (mg/L, X3) Removal %

Experimental Predicted

1 2 98.71 0.28 1.81 89.80 91.452 5 36.28 0.28 4.18 39.90 35.883 7 36.28 0.81 4.18 60.10 50.364 4 98.71 0.81 1.81 99.27 98.875 8 98.71 0.81 4.18 77.70 77.896 6 98.71 0.28 4.18 70.20 63.417 1 36.28 0.28 1.81 66.40 61.078 10 67.50 0.55 3.0 74.80 69.339 9 67.50 0.55 3.0 72.90 69.3310 3 36.28 0.81 1.81 69.80 68.5011 11 67.50 0.55 3.0 68.60 69.331 4 67.50 1.00 3.0 59.80 63.742 11 67.50 0.55 3.0 70.40 69.333 2 120.0 0.55 3.0 98.00 98.434 9 67.50 0.55 3.0 65.10 69.335 1 15.00 0.55 3.0 40.80 49.736 7 67.50 0.55 3.0 66.80 69.337 10 67.50 0.55 3.0 74.80 69.338 8 67.50 0.55 3.0 62.85 69.339 5 67.50 0.55 1.0 95.80 96.2410 3 67.50 0.10 3.0 39.90 45.32

11 6 67.50 0.55

2013). These observations were confirmed by other authorslike Bagda et al. (2013) and Ersanet al. (2013) focused on TCadsorption on cryogels which maximum removal observed atpH 9. In a study conducted by Chang et al. (2009) on tetracyclinesorption by mineral clay, palygorskite, reached maximum atpH 8–9.5. By considering that maximum adsorption was foundat pH 9, optimization of photocatalytic process was done bythree independent variables viz. contact time, initial TCH con-centration and catalyst dosage at constant pH 9.

As was expected in Fig. 8c and d, by initial TCH concen-

tration increasing a decrease was observed in TCH removaldue to decreasing the number of available reactive sites and

Table 4 – Results of ANOVA and estimated coefficients of mode

Source Adsorption process

Coefficient Std.error t-Value P-Value

Model 80.229 1.089 73.615 2.2 × 10−16

X1 6.7483 1.989 3.391 0.001777

X2 19.36 1.989 9.729 2.34 × 10−1

X3 19.238 1.989 9.668 2.74 × 10−1

X4 −16.541 1.989 −8.313 1.05 × 10−9

X1X3

X2X3 −15.27 4.873 −3.133 0.003551

X12 3.552 3.329 1.067 0.293478

X22 −4.042 3.329 −1.214 0.233077

X32 −16.492 3.329 −4.953 1.97 × 10−5

X42 3.787 3.329 1.137 0.263238

Model formula Df Sum Sq. Mean Sq. F value Pr (>

FO 4 6384.5 1596.13 67.192 1.15TWI (X1,X3)

TWI (X2,X3) 1 233.2 233.17 9.8158 0.00PQ 4 662.3 165.57 9.9698 0.00Residual 34 807.7 23.75

Lack of fit 15 442.7 29.51 1.5362 0.18Pure error 19 365.0 19.21

Adsorption: multiple R-squared: 0.9001, adjusted R-squared: 0.8737.Photocatalytic degradation: multiple R-squared: 0.9142, adjusted R-square

5.0 48.50 57.42

saturation of adsorption sites on BiOI (Chen et al., 2011).In adsorption process (Fig. 8c), by initial TCH concentrationfrom 1 to 5 mg/L increasing, its removal efficiency was dimin-ished from 96.25% to 65.28% at coded zero level of othervariables. The same trend was observed in photocatalyticprocess as shown in Fig. 8d. Photocatalytic degradation effi-ciency decreased from 95.8% to 48.5% with increasing initialTCH concentration from 1 to 5 mg/L.

The effect of BiOI dosages on TCH removal are shown inFig. 8b and e. As it clear from these figures, as BiOI dosage

increases from 0.1 to 2 g/L in adsorption process, TCH removalincreases up to 75% at constancy of other parameters (pH

l terms for TCH removal.

Photocatalytic degradation process

Coefficient Std.error t-Value P-Value

69.3305 2.2694 30.550 1.720 × 10−13

24.3459 2.9232 8.3284 1.436 × 10−6

1 9.2074 2.9232 3.1497 0.0076761 −19.4139 2.9232 −6.6412 1.610 × 10−5

−2.0153 6.4234 −0.3137 0.7586994.9851 6.4234 0.7761 0.4515894.7494 4.6159 1.0289 0.322283

−14.8006 4.6159 -3.2064 0.0068827.4994 4.6159 1.6247 0.128217

F) Df Sum Sq. Mean Sq. F value Pr (> F)

× 10−15 3 5091.1 1697.02 41.129 6.739 × 10−7

1 4.1 4.06 0.0984 0.75870355 1 24.9 24.85 0.6023 0.45159328 3 595.3 198.44 4.8095 0.01819

13 536.4 41.26692 6 396.2 66.03 3.296 0.07199

7 140.2 20.03

d: 0.8614.

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 225

Fig. 8 – The 3D surface plots of combined effects of independent variables in adsorption (a–c) and photocatalytic process (d,e

7bod0m1tdtsw

3

Kw

).

, time 32.5 min and TCH concentration 3 mg/L). This coulde attributed to the increase in surface area and numberf adsorption sites on adsorbent. By comparison, when theosage of BiOI in photocatalytic degradation increased from.1 to 0.7 g/L, TCH degradation reached up to 100% under illu-ination time 120 min and with more increasing dosage to

g/L, removal efficiency of TCH decreased. It can be deducedhat the increasing catalyst dosage in reaction system alwayso not lead to increasing degradation efficiency, because ofhe preventing the light entrance and penetration into theolution. The achieved results in this study were in agreementith those obtained in other studies (Gao et al., 2017).

.4. Kinetic modeling

inetic studies of adsorption have valuable information,hich are useful in understanding the mechanism and inter-

action between adsorbent and adsorbate. Three linear classickinetic models including pseudo-first-order, pseudo-second-order, and intraparticle diffusion used to model kinetic datacan be given as follows (Asfaram et al., 2015; Guler andSarioglu, 2014):

Log (qe − qt) = Logqe − k1t (6)

tqt

= 1

k2q2e

+ tqe

(7)

qt = kpt0.5 + C (8)

where qe is adsorption capacity (mg/g) at equilibrium, qtrepresents the amount of TCH adsorbed onto BiOI (mg/g)at time intervals (min), k1 (min−1), k2 (g/mg min) and kp

(g mg−1 min−0.5) are rate constants. C is constant based on thethickness of the boundary layer.

226 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

Fig. 9 – Pseudo-second-order kinetic plots for TCH

adsorption on a) BiOI-ST and b) BiOI-H.

The kinetic parameters of models are summarized inTable 5. The ability of kinetic models to describe experimen-tal data was tested by plotting log (qe − qt) against t, t/qt

against t and qt versus t−0.5 for pseudo-first-order, pseudo-second-order (Fig. 9) and intraparticle diffusion, respectively.According to the correlation coefficients of models in Table 5,in both BiOI-H and BiOI-ST pseudo-second-order model withR2 > 0.98 could well explain experimental data of adsorptionin all initial concentration ranges. Furthermore, the adsorp-tion capacity values predicted by pseudo-second-order modelas 3.6523 mg/g for BiOI-ST and 3.1046 mg/g for BiOI-H arecloser to the experimental ones of 3.629 mg/g for BiOI-STand 3.008 mg/g for BiOI-H toward to pseudo-first-order model.These results implied that the chemisorption as the ratelimiting step controls sorption process (Nawi et al., 2010).Adsorption kinetics of TCH on two prepared BiOI showed thatthe adsorption process is very fast and reached to equilibrium

within 40 min. This rapid adsorption can be due to the highnumber of adsorption sites on the surface of adsorbent (Zhang

Table 5 – The calculated parameters of kinetic models.

Concentration (mg/L)

BiOI-ST

1 2 3 4 5

qe, exp (mg/g) 0.6215 1.1680 1.8890 2.6850 3Pseudo-first orderqe (mg/g) 0.0805 0.1649 0.2891 0.3331 0k1 (min−1) 0.0515 0.0375 0.0460 0.0704 0R2 0.6145 0.2848 0.6795 0.6651 0

Pseudo-second orderqe (mg/g) 0.6258 1.1536 1.8892 2.6961 3k2 (g/mg min) 2.8066 1.4056 0.6786 0.8751 0R2 0.9996 0.9983 0.9987 0.9998 0

Intraparticle diffusionKp (g mg−1 min−0.5) 0.0158 0.0365 0.0502 0.0743 0C 0.5205 0.9007 1.4989 2.1963 2R2 0.7520 0.5044 0.7875 0.7092 0

et al., 2015). As shown in Table 5, the pseudo-second-orderrate constants reduced with increasing initial TCH concen-tration in both BiOI implying reduction of adsorption rate.By comparing the adsorption kinetic of two prepared BiOI wefound that the k2 values of BiOI-ST are about 3 times higherthan BiOI-H, meaning that BiOI-ST is a more quick adsorbentthan BiOI-H. This can be due to the higher surface area ofBiOI-ST (nearly 4 times) and subsequently the availability ofthe more adsorption sites on BiOI-ST. additionally, accordingto the experimental and pseudo-second-order kinetic data,a greater adsorption capacity of BiOI-ST for TCH suggest ahigher removal efficiency than BiOI-H.

3.5. Isotherm modeling

Isotherm studies establish a relation between the remainingconcentration of adsorbate at the bulk after reaching to equi-librium (Ce) and the adsorbed amount on the adsorbent (Bagdaet al., 2013). Hence, in this study, three isotherm models con-sist of Langmuir, Freundlich and Dubinin–Radushkevich wereemployed to fit the equilibrium data. Langmuir isotherm isbased on the assumption that the adsorption is monolayerand the adsorption sites are independence from each other(Bagda et al., 2013; Ersan,2016). The Langmuir isotherm can beshown in linear form as follows:

Ce

qe= 1

bQ0+ 1

Q0Ce (9)

where qe (mg/g) and Ce (mg/L) are TCH concentration at equi-librium on adsorbent and solution bulk, respectively. b (L/mg)is constant related to intensity of the adsorption and Q0 (mg/g)is constant related to adsorption capacity that can be achievedfrom the intercept and slope of plot Ce/qe versus Ce respec-tively.

Freundlich isotherm is used to describe equilibrium on het-erogeneous surfaces and multilayer adsorption (Bagda et al.,2013; Ersan,2016). The empirical Freundlich isotherm can beexpressed as linear form:

Logqe = LogKF +(

1n

)LogCe (10)

where KF (mg g−1) and 1/n are Freundlich constants. KF isrelated to adsorption capacity of adsorbent. The slope of plot

Adsorbent

BiOI-H

1 2 3 4 5

.6300 0.4475 1.0690 1.7901 2.5857 3.0083

.7507 0.1222 0.1081 0.6736 0.7485 0.8126

.0674 0.0239 −0.0446 0.0191 0.1296 0.0225

.9222 0.1517 0.2518 0.2144 0.4315 0.1635

.6523 0.4418 1.0679 1.5740 2.5713 3.1046

.3132 0.9772 0.4034 0.6522 0.1905 0.1205

.9988 0.9851 0.9874 0.9823 0.9803 0.9868

.1114 0.0323 0.0205 0.005 0.068 0.1131

.7865 0.2137 0.8432 1.4832 1.9715 2.1072

.8770 0.6211 0.1194 0.0028 0.1586 0.2643

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 227

isoth

Lhbue

acSh

l

wcp

ε

tme

E

awc

tiTh

vorable, but the values were in good agreement with those

Table 6 – The constants and correlation coefficients ofLangmuir, Freundlich and D–R isotherms for TCHadsorption.

Isotherm Parameters Adsorbent

BiOI-ST BiOI-H

Langmuir Q0 (mg/g) −10.917 −0.3597b (L mg–1) −0.152 −0.6925RL 4.175 −0.4060R2 0.6302 0.7714

Freundlich n 0.5393 0.2362Kf (mg g–1) (mg–1)1/n 2.2468 0.8211R2 0.9626 0.9504

D–R � (mol2/J2) 1.667 × 10−6 1.111 × 10−6

qm (mg/g) 32.287 24.8756

Fig. 10 – Langmuir (a), Freundlich (b) and D–R (c)

og qe against Log Ce, 1/n, indicates adsorption intensity andas a range between 0 and 1. The values of 1/n higher than 1,etween 0 and 1 and equal to zero reflect that adsorption isnfavorable, favorable and irreversible, respectively (Dehghanit al., 2017d).

The Dubinin–Radushkevich (D–R) isotherm model can bepplied to characterize adsorption process as physical andhemical and estimate free energy of adsorption (Guler andarioglu, 2014; Rangabhashiyam et al., 2014). The D–R modelas a linear form as below:

nqe = lnqm − ˇε2 (11)

here qm (mg/g) is maximum adsorption capacity, is a coeffi-ient related to mean free energy of adsorption and ε is Polanyiotential that can be calculated as:

= RTln

(1 + 1

Ce

)(12)

where R and T are the gas constant (8.314 J/mol K) and theemperature (K), respectively. The constant was used to esti-

ate the free energy E (kJ/mol) of adsorption by the followingquation:

= 1√−2ˇ

(13)

The values of E between 8 and 16 kJ/mol indicate that thedsorption process conform by chemical ion-exchange nature,hile in the values of E less than 8 kJ/mol, the adsorption pro-

ess may be physical in nature (Guler and Sarioglu, 2014).The isotherm constants for selected models and correla-

ion coefficients are shown in Table 6 and the plots of threesotherm models are presented in Fig. 10. It is obvious from

able 6 that the both Freundlich and D–R isotherms showigher R2 than the Langmuir isotherm and the R2 value of

erm plots for TCH adsorption on BiOI samples.

D–R isotherm was somewhat higher than that of Freundlichfor both BiOI-ST and BiOI-H. This demonstrated that TCHadsorption data were well fitted to both Freundlich and D–Risotherms having values of R2 0.962 and 0.984 for BiOI-ST and0.95 and 0.963 for BiOI-H, respectively. Moreover, maximumadsorption capacity of TCH suggested by isotherm of D–R forBiOI-ST and BiOI-H was 32.287 and 24.875 mg/g, respectively. Itseems that the Freundlich and D–R isotherms are more capa-ble than to the Langmuir isotherm to fit experimental databecause of the following reason. First, the negative calculatedvalues of qmax from Langmuir are significantly different fromthe obtained actual ones. Second, the values of b obtainedfrom Langmuir isotherm are inconsistent. This may be dueto fact that the adsorption of TCH on BiOI follows multilayeradsorption instead of monolayer adsorption. Although theheterogeneity value, 1/n, of Freundlich model was found to behigher than 1, indicating that the adsorption process is unfa-

E (kJ/mol) 0.547 0.670R2 0.9844 0.963

228 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

ots fo

Fig. 11 – Pseudo-first order kinetic pl

reported by Li et al. (2017). According to D–R isotherm model,the value of mean free energy was estimated to be 0.547 forBiOI-ST and 0.670 kJ/mol for BiOI-H that suggesting the phys-ical characteristics of the adsorption in both them.

3.6. Degradation kinetic

To further compare photocatalytic activity of two pre-pared BiOI, degradation kinetic study was performed.Langmuir–Hinshelwood kinetic model is commonly usedmodel for exploring the effect of initial concentration of pol-lutant on photocatalytic activity of catalysts. The L–H kineticmodel can be summarized as a pseudo-first order kineticmodel at low concentration of TCH, which expressed as:

Ln

(CtC0

)= −Kappt (14)

where C0 and Ct are the initial concentration of TCH (mg L−1)and the residual concentration in the sample at time t (mg L−1).Kapp is the apparent pseudo-first-order rate constant (min−1).The linear plot of Ln (Ct/C0) against illumination time undertwo different initial TCH concentration and the kinetic param-eters are given in Fig. 11 and Table 7, respectively. As shown inTable 7, the correlation coefficients (R2) values of kinetic modelwere higher than 0.93 in initial concentration 3 and 5 mg L−1

for both BiOI, which confirm the applicability of the pseudo-first-order kinetic model to fit the experimental data. It can beobserved that the degradation rate is as a function of the TCHinitial concentration so that with increasing initial concentra-tion of TCH, the values of Kapp decreased. As expected, BiOI-STexhibits the higher photocatalytic activity in TCH degrada-tion than BiOI-H because of the greater values of Kapp. Thiscan be explained by the difference in synthesis method oftwo kinds of BiOI. According to the previous studies, the mostsuitable methodology for synthesis of BiOI microstructures issolvothermal method, in which the high pressure and tem-perature can be considered as the crucial factors to influence

the morphology of BiOI (Xu et al., 2013). The solvothermal con-ditions improve the physicochemical behaviors of the solvent

Table 7 – The rate constant and correlation coefficient ofpseudo-first order kinetic model for TCH degradation.

Concentration (mg/L) Catalyst

BiOI-ST BiOI-H

3 5 3 5

K 0.0223 0.0147 0.015 0.0105R2 0.9365 0.9439 0.9715 0.9301

r TCH degradation by BiOI samples.

mainly dielectric constant (Xu et al., 2013). With decreasingthe dielectric constant, the band gap and crystal size decreaseand photocatalytic activity of catalyst increase (Farrukh et al.,2016). Then, the smaller band gap and greater surface area ofBiOI-ST are indicative of its more photocatalytic activity com-pared to BiOI-H. The high Surface area can absorb more lightand provide more adsorption sites, which improve photocat-alytic performance (Jamil et al., 2015; Hao et al., 2012).

4. Conclusion

Briefly, a BiOI catalyst with simultaneousadsorption–photocatalytic properties was synthesized bysolvothermal method, which can be used to treat hospitalwastewaters. Thermal step in BiOI-ST synthesis process hada great effect on its surface area, morphology and photo-catalytic ability. According to the results of characterizationtests, thermal treatment could well reduce the thickness ofnanosheets and energy band gap in BiOI-ST sample. Opti-mization and modeling of TCH adsorption and photocatalyticdegradation was carried out using CCD under RSM. Accordingto this, a reduced quadratic model was suggested to predictthe response values for each process. The optimum condi-tions of TCH removal obtained by solver program were as:TCH initial concentration of 2.1 mg/L, BiOI of 1.5 g/L, pH of8.5 and time of 37.5 min for TCH adsorption process and TCHinitial concentration of 2 mg/L, BiOI of 0.68 g/L and time of101.5 min in TCH photocatalytic degradation.

Acknowledgment

This research was supported by the Tehran University ofMedical Sciences, Institute for Environmental Research underproject no. 94-03-46-30017. The authors would like to appreci-ate the financial supports by them.

References

Acosta, R., Fierro, V., Martinez de Yuso, A., Nabarlatz, D., Celzard,A., 2016. Tetracycline adsorption onto activated carbonsproduced by KOH activation of tyre pyrolysis char.Chemosphere 149, 168–176.

Asfaram, A., Ghaedi, M., Goudarzi, A., Rajabi, M., 2015. Responsesurface methodology approach for optimization ofsimultaneous dye and metal ion ultrasound-assistedadsorption onto Mn doped Fe3O4-NPs loaded on AC: kineticand isothermal studies. Dalton Trans. 44, 14707–14723.

Asfaram, A., Ghaedi, M., Yousefi, F., Dastkhoon, M., 2016.

Experimental design and modeling of ultrasound assistedsimultaneous adsorption of cationic dyes onto ZnS:

chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230 229

B

C

C

C

C

D

D

D

D

D

D

D

E

E

F

G

G

Mn-NPs-AC from binary mixture. Ultrason Sonochem. 33,77–89.

agda, E., Ersan, M., Bagda, E., 2013. Investigation of adsorptiveremoval of tetracycline with sponge like, Rosa canina gallextract modified, polyacrylamide cryogels. J. Environ. Chem.Eng. 1, 1079–1084.

hang, P.H., Li, Z., Yu, T.L., Munkhbayer, S., Kuo, T.H., Hung, Y.C.,Jean, J.S., Lin, K.H., 2009. Sorptive removal of tetracycline fromwater by palygorskite. J. Hazard. Mater. 165, 148–155.

hen, W.R., Huang, C.H., 2010. Adsorption and transformation oftetracycline antibiotics with aluminum oxide. Chemosphere79, 779–785.

hen, Y., Fang, J., Lu, S., Xu, W., Liu, Z., Xu, X., Fang, Z., 2015.One-step hydrothermal synthesis of BiOI/Bi2WO6 hierarchicalheterostructure with highly photocatalytic activity. J. Chem.Technol. Biotechnol. 90, 947–954.

hen, H., Luo, H., Lan, Y., Dong, T., Hu, B., Wang, Y., 2011. Removalof tetracycline from aqueous solutions usingpolyvinylpyrrolidone (PVP-K30) modified nanoscale zerovalent iron. J. Hazard. Mater. 192, 44–53.

ehghani, M.H., Taher, M.M., Bajpai, A.K., Heibati, B., Tyagi, I.,Asif, M., Agarwal, S., Gupta, V.K., 2015. Removal of noxiousCr(VI) ions using single-walled carbon nanotubes andmulti-walled carbon nanotubes. Chem. Eng. J. 279, 344–352.

ehghani, M.H., Mostofi, M., Alimohammadi, M., McKay, G.,Yetilmezsoy, K., Albadarin, A.B., Heibati, B., Al-Ghouti, M.A.,2016a. High-performance removal of toxic phenol bysingle-walled and multi-walled carbon nanotubes: kinetics,adsorption, mechanism and optimization studies. J. Ind. Eng.Chem. 35, 63–74.

ehghani, M.H., Ghadermazi, M., Bhatnagar, A., Sadighara, P.,Jahed-Khaniki, G., Heibati, B., Mckay, G., 2016b. Adsorptiveremoval of endocrine disrupting bisphenol A from aqueoussolution using chitosan. J. Environ. Chem. Eng. 4, 2647–2655.

ehghani, M.H., Niasar, Z.S., Mehrnia, M.R., Shayeghi, M.,Al-Ghouti, M.A., Heibati, B., Mckay, G., 2017a. Optimizing theremoval of organophosphorus pesticide malathion fromwater using multi-walled carbon nanotubes. Chem. Eng. J.310, 22–32.

ehghani, M.H., Dehghan, A., Najafpoor, A., 2017b. RemovingReactive Red 120 and 196 using chitosan/zeolite compositefrom aqueous solutions: kinetics, isotherms, and processoptimization. J. Ind. Eng. Chem. 51, 185–195.

ehghani, M.H., Zarei, A., Mesdaghinia, A., Nabizadeh, R.,Alimohammadi, M., Afsharnia, M., 2017c. Response surfacemodeling, isotherm, thermodynamic and optimization studyof arsenic(V) removal from aqueous solutions using modifiedbentonite-chitosan (MBC). Korean J. Chem. Eng. 34, 757–767.

ehghani, M.H., Dehghan, A., Alidadi, H., Dolatabadi, M.,Mehrabpour, M., Converti, A., 2017d. Removal of methyleneblue dye from aqueous solutions by a new chitosan/zeolitecomposite from shrimp waste: kinetic and equilibrium study.Korean J. Chem. Eng. 34, 1699–1707.

rsan, M., Bagda, E., Bagda, E., 2013. Investigation of kinetic andthermodynamic characteristics of removal of tetracycline withsponge like, tannin based cryogels. Colloid Surf. B 104, 75–82.

rsan, M., 2016. Removal of tetracycline using new biocompositesfrom aqueous solutions. Desalin. Water Treat. 57, 9982–9992.

arrukh, M.A., Muneer, I., Butt, K.M., Batool, S., Fakhar, N., 2016.Effect of dielectric constant of solvents on the particle sizeand bandgap of La/SnO2-TiO2 nanoparticles and theircatalytic properties. J. Chin. Chem. Soc. 63 (12), 952–959,http://dx.doi.org/10.1002/jccs.201600205.

ao, Y., Li, Y., Zhang, L., Huang, H., Hu, J., Shah, S.M., Su, X., 2012.Adsorption and removal of tetracycline antibiotics fromaqueous solution by graphene oxide. J. Colloid Interface Sci.368, 540–546.

ao, S., Guo, C., Lv, J., Wang, Q., Zhang, Y., Hou, S., Gao, J., Xu, J.,2017. A novel 3D hollow magnetic Fe3O4/BiOI heterojunctionwith enhanced photocatalytic performance for bisphenol Adegradation. Chem. Eng. J. 307, 1055–1065.

Ge, S., Zhao, K., Zhang, L., 2012. Microstructure-dependentphotoelectrochemical and photocatalytic properties of BiOI. J.Nanopart. Res. 14, 1015–1025.

Guler, U.A., Sarioglu, M., 2014. Removal of tetracycline fromwastewater using pumice stone: equilibrium, kinetic andthermodynamic studies. J. Environ. Health Sci. Eng. 12, 79–89.

Han, A., Chian, S.F., Toy, X.Y., Sun, J., Jaenicke, S., Chuah, G.K.,2015. Bismuth oxyiodide heterojunctions in photocatalyticdegradation of phenolic molecules. Res. Chem. Intermed. 41,9509–9520.

Hao, R., Xiao, X., Zuo, X., Nan, J., Zhang, W., 2012. Efficientadsorption and visible-light photocatalytic degradation oftetracycline hydrochloride using mesoporous BiOImicrospheres. J. Hazard. Mater. 209–210, 137–145.

He, R., Cao, S., Guo, D., Cheng, B., Wageh, S., Al-Ghamdi, A.A., Yu,J., 2015. 3D BiOI–GO composite with enhanced photocatalyticperformance for phenol degradation under visible-light.Ceram. Int. 41, 3511–3517.

Jamil, T.S., Mansor, E.S., El-Lieth, M.A., 2015. Photocatalyticinactivation of E. coli using nano-size bismuth oxyiodidephotocatalysts under visible light. J. Environ. Chem. Eng. 3,2463–2471.

Jia, S., Yang, Z., Yang, W., Zhang, T., Zhang, S., Yang, X., Dong, Y.,Wu, J., Wang, Y., 2016. Removal of Cu(II) and tetracycline usingan aromatic rings-functionalized chitosan-based flocculant:enhanced interaction between the flocculant and theantibiotic. Chem. Eng. J. 283, 495–503.

Koyuncu, I., Arikan, O.A., Wiesner, M.R., Rice, C., 2008. Removal ofhormones and antibiotics by nanofiltration membranes. J.Membr. Sci. 309, 94–101.

Lee, W.W., Lu, C.S., Chuang, C.W., Chen, Y.J., Fu, J.Y., Siao, C.W.,Chen, C.C., 2015. Synthesis of bismuth oxyiodides and theircomposites characterization, photocatalytic activity, anddegraded mechanisms. RSC Adv. 5, 23450–23463.

Li, Y., Wang, J., Yao, H., Dang, L., Li, Z., 2011. Efficientdecomposition of organic compounds and reactionmechanism with BiOI photocatalyst under visible lightirradiation. J. Mol. Catal. A 334, 116–122.

Li, G., Guo, Y., Zhao, W., 2017. Efficient adsorption removal oftetracycline by layered carbon particles prepared fromseaweed biomass. Environ. Prog. Sustain. Energy 36, 59–65.

Lin, H., Zhou, C., Cao, J., Chen, S., 2014. Ethylene glycol-assistedsynthesis, photoelectrochemical and photocatalyticproperties of BiOI microflowers. Chin. Sci. Bull. 59, 3420–3426.

Liu, H., Yang, Y., Kang, J., Fan, M., Qu, J., 2012. Removal oftetracycline from water by Fe–Mn binary oxide. J. Environ. Sci.24, 242–247.

Liu, H., Cao, W.R., Su, Y., Chen, Z., 2013. Bismuthoxyiodide–graphene nanocomposites with high visible lightphotocatalytic activity. J. Colloid Interface Sci. 398, 161–167.

Mehraj, O., Pirzada, B.M., Mir, N.A., Khan, M.Z., Sabir, S., 2016. Ahighly efficient visible-light-driven novel p–n junctionFe2O3/BiOI photocatalyst: surface decoration of BiOInanosheets with Fe2O3 nanoparticles. Appl. Surf. Sci. 387,642–651.

Nawi, M.A., Sabar, S., Jawad, A.H., Sheilatina, Wan Ngah, W.S.,2010. Adsorption of Reactive Red 4 by immobilized chitosanon glass plates: towards the design of immobilizedTiO2–chitosan synergistic photocatalyst-adsorption bilayersystem. Biochem. Eng. J. 49, 317–325.

Oladoja, N.A., Adelagun, R.O.A., Ahmad, A.L., Unuabonah, E.I.,Bello, H.A., 2014. Preparation of magnetic, macro-reticulatedcross-linked chitosan for tetracycline removal from aquaticsystems. Colloid Surf. B 117, 51–59.

Oskoei, V., Dehghani, M.H., Nazmara, S., Heibati, B., Asif, M.,Tyagi, I., Agarwal, S., Gupta, V.K., 2016. Removal of humic acidfrom aqueous solution using UV/ZnO nano-photocatalysisand adsorption. J. Mol. Liq. 213, 374–380.

Oturan, N., Wu, J., Zhang, H., Sharma, V.K., Oturan, M.A., 2013.Electrocatalytic destruction of the antibiotic tetracycline inaqueous medium by electrochemical advanced oxidation

processes: effect of electrode materials. Appl. Catal. B140–141, 92–97.

230 chemical engineering research and design 1 2 9 ( 2 0 1 8 ) 217–230

degradation of tetracycline in aqueous solution by nanosizedTiO2. Chemosphere 92, 925–932.

Pan, M., Zhang, H., Gao, G., Liu, L., Chen, W., 2015.Facet-dependent catalytic activity of nanosheet-assembledbismuth oxyiodide microspheres in degradation of bisphenolA. Environ. Sci. Technol. 49, 6240–6248.

Rangabhashiyam, S., Anu, N., Giri Nandagopal, M.S., Selvaraju,N., 2014. Relevance of isotherm models in biosorption ofpollutants by agricultural byproducts. J. Environ. Chem. Eng. 2,398–414.

Senthilnathan, J., Philip, L., 2010. Photocatalytic degradation oflindane under UV and visible light using N-doped TiO2. Chem.Eng. J. 161, 83–92.

Vinoth, R., Babu, S.G., Ramachandran, R., Neppolian, B., 2017.Bismuth oxyiodide incorporated reduced graphene oxidenanocomposite material as an efficient photocatalyst forvisible light assisted degradation of organic pollutants. Appl.Surf. Sci. 418, 163–170.

Weng, B., Xu, F., Xu, J., 2014. Hierarchical structures constructedby BiOX (X = Cl, I) nanosheets on CNTs/carbon compositefibers for improved photocatalytic degradation of methylorange. J. Nanopart. Res. 16, 2766–2778.

Xiao, G., Su, H., Tan, T., 2015. Synthesis of core–shell bioaffinitychitosan–TiO2 composite and its environmental applications.J. Hazard. Mater. 283, 888–896.

Xiao, X., Hao, R., Liang, M., Zuo, X., Nan, J., Li, L., Zhang, W., 2012.One-pot solvothermal synthesis of three-dimensional (3D)BiOI/BiOCl composites with enhanced visible-light

photocatalytic activities for the degradation of bisphenol-A. J.Hazard. Mater. 233–234, 122–130.

Xu, X.R., Li, X.Y., 2010. Sorption and desorption of antibiotictetracycline on marine sediments. Chemosphere 78, 430–436.

Xu, Y.S., Zhang, Z.J., Zhang, W.D., 2013. Facile preparation ofheterostructured Bi2O3/Bi2MoO6 hollow microspheres withenhanced visible-light-driven photocatalytic andantimicrobial activity. Mater. Res. Bull. 48, 1420–1427.

Yu, X., Lu, Z., Wu, D., Yu, P., He, M., Chen, T., Shi, W., Huo, P., Yan,Y., Feng, Y., 2014. Heteropolyacid–chitosan/TiO2 compositesfor the degradation of tetracycline hydrochloride solution.React. Kinet. Mech. Catal. 111, 347–360.

Zhang, B., Ji, G., Gondal, M.A., Liu, Y., Zhang, X., Chang, X., Li, N.,2013. Rapid adsorption properties of flower-like BiOInanoplates synthesized via a simple EG-assistedsolvothermal process. J. Nanopart. Res. 15, 1773–1781.

Zhang, D., 2014. Heterostructural BiOI/TiO2 composite withhighly enhanced visible light photocatalytic performance.Russ. J. Phys. Chem. A 88, 2476–2485.

Zhang, Z., Lan, H., Liu, H., Qu, J., 2015. Removal of tetracyclineantibiotics from aqueous solution by amino-Fe(III)functionalized SBA15. Colloid Surf. A 471, 133–138.

Zhao, Y., Geng, J., Wang, X., Gu, X., Gao, S., 2011. Adsorption oftetracycline onto goethite in the presence of metal cationsand humic substances. J. Colloid Interface Sci. 361, 247–251.

Zhu, X.D., Wang, Y.J., Sun, R.J., Zhou, D.M., 2013. Photocatalytic