Carbon Modified TiO2 Photocatalyst with Enhanced Adsorptivity for Dyes from Water

A new photocatalyst was obtained by modification of commercial anatase TiO₂ (Police, Poland) in a pressure reactor in an ethanol atmosphere at 120 °C for 4 h. The photocatalytic activity of the new material was tested during three azo dyes decomposition: monoazo (Reactive Red 198), diazo (Reactive Black 5) and poliazodye (Direct Green 99). The obtained photocatalyst had new bands at 1,440 cm^?1 attributed to CO groups. UV–Vis/DR spectra of the photocatalyst also were changing and had an insignificant decrease in the visible region of the spectra. The amount of hydroxyl radicals produced on carbon-modified TiO₂ was a little higher than for the pristine one. The carbon modification also changes the Freundlich model of dyes adsorption to Langmuir model of adsorption. Additionally, it increases the monolayer capacity of modified TiO₂. As a result we observed a clear increase of the photocatalytic activity of carbon-modified TiO₂ sample.     

Lifetime of Carbon-Modified TiO2 Photocatalysts Under UV Light Irradiation

Carbon-modified photocatalyst was obtained by modification of the commercial anatase TiO₂ (Police, Poland) in a pressure reactor in an ethanol atmosphere at 120 °C for 4 h. The activity was tested during monoazo dye decomposition under UV light irradiation (Reactive Red 198 with λ_max = 516 nm). The reusability aspect of carbon-modified TiO₂ photocatalysts was predominantly studied. Using the additional aeration process caused to stabilization the “decolourisation time” of aqueous solution of Reactive Red 198. To compare the activity of obtained material the commercial TiO₂ P25 was used and only on its surface the presence of carbon deposits were observed.     

Integration of photocatalysis and membrane distillation for removal of mono- and poly-azo dyes from water

The paper reports investigations on the application of anatase-phase TiO₂ for the removal of azo dyes in a hybrid system coupling photocatalysis with direct contact membrane distillation (DCMD, MD). The process was conducted in a laboratory-scale installation equipped with a PP capillary module. The influence of reaction temperature and initial concentration of azo dyes on the effectiveness of their photodegradation was especially investigated. Two mono-azo dyes: Acid Red 18 (AR18) and Acid Yellow 36 (AY36) and one poly-azo dye, Direct Green 99 (DG99) were applied as model compounds. The increase of the reaction temperature from 313 to 333 K resulted in an improvement of the efficiency of photodecomposition of the dyes, as was found on the basis of changes of their masses in the feed solution. The comparison of the results obtained during photocatalysis alone and hybrid photocatalysis-MD process revealed that the reduction of feed volume in MD did not affect the photodegradation rate of the azo dyes. An improvement of the effectiveness of the degradation of dyes was obtained by an application of solutions with lower initial concentration (10 instead of 30 mg/dm³). Regardless of the process parameters applied, the product (distillate) was almost pure water with conductivity lower than 0.3 mS/m and pH above 5.2.     

Solar-light-induced photocatalytic decomposition of two azo dyes on new TiO2 photocatalyst containing nitrogen

The photocatalytic decolourisation of two azo dyes—Reactive Red 198 and Direct Green 99—in an aqueous solution by the artificial visible light radiation was investigated. The industrial metatitanic acid (H₂TiO₃) obtained directly from the sulphate technology installation was N-doped and used as photocatalyst. H₂TiO₃ was calcinated at different temperatures, ranging from 300 to 500 °C, for 4 or 20 h, respectively, in an ammonia atmosphere. The UV–vis/DR spectra of the modified catalysts exhibited an additional maximum in the vis region (λ ≈ 476.8 nm, E_G = 2.60 eV for catalysts calcinated for 4 h and λ ≈ 479.5 nm, E_G = 2.59 eV for catalysts calcinated for 20 h, which may be due to the presence of nitrogen in TiO₂ particles. The chemical structure of the modified photocatalysts was investigated using FTIR/DRS spectroscopy and the presence of nitrogen was confirmed. A photocatalytic activity of the investigated catalysts was determined on the basis of a decomposition rate of azo dyes. The decomposition of Reactive Red 99 increased with increasing the calcination temperature of photocatalysts, whereas the activity of the prepared photocatalysts towards Direct Green 198 degradation was as follows: 300–20 h < 400–20 h < 500–20 h < 300–4h < 400–4 h < 500–4 h. Both, the calcination time and temperature had no influence on the amount of nitrogen-doped into TiO₂ structure. The inversely proportional linear dependence between the decomposition rates of azo dyes and the intensity of the band attributed to the hydroxyl groups for both dissociated water and molecularly adsorbed water was observed. With increasing temperature of calcinations, the amount of the hydroxyl groups decreased, whereas the decomposition of azo dyes increased.     

The pH influence on photocatalytic decomposition of organic dyes over A11 and P25 titanium dioxide

The photocatalytic removal (decomposition+adsorption) of four azodyes (Reactive Red 198, Acid Black 1, Acid Blue 7 and Direct Green 99) in water was investigated using Tytanpol A11 (“Police” Chemical Factory, Poland) and Degussa P25 (“Degussa”, Germany) as photocatalysts. The effect of pH of the reaction solution has been examined. The degree of the dye removal in the solution was measured by UV-Vis spectroscopy. Photodecomposition of dye on photocatalyst surface was monitored by FTIR spectroscopy. A11 photocatalyst has lower activity in the reaction of photocatalytic decomposition of organic dyes than Degussa P25. The photocatalytic decomposition of the dyes takes place on the photocatalyst surface at pH=2 while at pH=12 photocatalytic reaction proceeds via photogenerated hydroxyl radicals for both A11 and P25.     

Decolorization and degradation of reactive azo dyes via heterogeneous photocatalytic processes

Reactive dyes are extensively used in textile industry in the last years due to their superior performance, but they are environmentally hazardous and difficult to treat effectively by classical methods. In the present work, the decolorization and degradation of four commercial reactive azo dyes, namely Remazol Red RR, Remazol Yellow RR, Procion Crimson H-exl and Procion Yellow H-exl, were studied using photocatalytic processes (TiO₂/UV and TiO₂/UV/H₂O₂). Decolorization and degradation were found to strongly depend on the system parameters (TiO₂ loading, dye and H₂O₂ initial concentrations, and pH). Decolorization efficiency (%) sharply increases with increasing the TiO₂ loading, especially up to 1 g/L, as well as with decreasing the initial dye concentration from 250 down to 50 mg/L. At pH = 3, a > 90% decolorization of all dyes can be achieved in only 15 min. Addition of H₂O₂ increases the decolorization rates up to an optimum value (97.9% Remazol Red RR decolorization at 12 min irradiation, with a 0.5%w/w initial H₂O₂ concentration and pH = 3). Among the four dyes examined, significant differences in decolorization and degradation rates were revealed, but decolorization and degradation efficiencies up to 100% (in 25 min and 4 h respectively) are possible with proper combinations of the system parameters.     

Removal of reactive dyes from wastewater by acrylate polymer beads bearing amino groups: isotherm and kinetic studies

The aim of this study was to prepare a novel resin for the removal of reactive dyes from aqueous media. To prepare the resin, poly(2‐hydroxyethyl methacrylate/ethylene glycol dimethacrylate) beads were grafted with poly(glycidyl methacrylate) by surface‐initiated atom transfer radical polymerisation. Epoxy groups of the grafted polymer were modified with tris(2‐aminoethyl)amine ligand. The modified resin was characterised by swelling studies, FT‐IR and SEM. Three different reactive dyes were selected (CI Reactive Brown 10, CI Reactive Red 120 and CI Reactive Green 5) and used in the removal studies. The effects of pH, temperature, ionic strength and initial dye concentration on the adsorption capacity of the resin were investigated. The adsorption capacity of the resin for Reactive Brown 10, Reactive Red 120 and Reactive Green 5 was 0.029 ± 0.010, 0.032 ± 0.0019 and 0.042 ± 0.0013 mmol/g resin (34.1 ± 1.2, 47.6 ± 2.3 and 69.3 ± 1.7 mg/g resin) respectively. The equilibrium adsorption data were analysed by Langmuir, Dubinin–Radushkevich, Freundlich and Temkin isotherm models. A good fit was found between the Langmuir isotherm and data for the three dyes on resin. The adsorption kinetic data were modelled using pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion kinetic equations. It was found that the pseudo‐second‐order equation could describe the adsorption kinetics. The results indicated that the modified resin is an attractive alternative for removing reactive dyes from wastewater.     

Adsorption of Textile Dye on Zinc Stannate Oxide: Equilibrium,Kinetic and Thermodynamics Studies

Zn₂SnO₄ powder was prepared by hydrothermal process at 200°C for 12 h. The material was characterized by X-ray-diffraction and surface area. The synthesized sample presented a pure phase and a surface area of 48.8 m² · g^?1. It was used as adsorbent to remove the Reactive Red 141 that is a azo textile dye. The adsorption kinetics of the textile dye on Zn₂SnO₄ followed the pseudo-second-order model. The adsorption process was found to be controlled by both external mass transfer and intraparticle diffusion. The equilibrium data were in good agreement with both Langmuir and Freundlich isotherms. Thermodynamic parameters were calculated, and the results revealed that the adsorption process is endothermic in nature, with weak forces of the Van der Walls acting.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Comparison of oxidation efficiency of disperse dyes by chemical and photoelectrocatalytic chlorination and removal of mutagenic activity

Degradation of Disperse Orange 1, Disperse Red 1 and Disperse Red 13 dyes has been performed using electrochemical oxidation on Pt electrode, chemical chlorination and photoelectrochemical oxidation on Ti/TiO₂ thin film electrodes in NaCl or Na₂SO₄ medium. 100% discoloration was obtained for all tested methods after 1 h of treatment. Faster color removal was obtained by photoelectrocatalytic oxidation in 0.1 mol L⁻¹ NaCl pH 4.0 under UV light and an applied potential of +1.0 V (vs SCE reference electrode), which indicates also values around 60% of TOC removal. The conventional chlorination method and electrochemical oxidation on Pt electrode resulted in negligible reduction of TOC removal. All dyes showed positive mutagenic activity in the Salmonella/microsome assay with the strain TA98 in the absence and presence of S9 (exogenous metabolic activation). Nevertheless, there is complete reduction of the mutagenic activity after 1 h of photoelectrocatalytic oxidation, suggesting that this process would be good option to remove disperse azo dyes from aqueous media.     

Removal of Reactive Red 198 from aqueous solution by combined method multi-walled carbon nanotubes and zero-valent iron:Equilibrium,kinetics, and thermodynamic

Dyes often include toxic,carcinogenic compounds and are harmful to humans' health.Therefore,removal of dyes from textile industry wastewater is essential.The present study aimed to evaluate the efficiency of the combination of zero valent iron(ZVI) powder and multi-walled carbon nanotubes(MWCNTs) in the removal of Reactive Red 198(RR198) dye from aqueous solution.This applied research was performed in a batch system in the laboratory scale.This study investigated the effect of various factors influencing dye removal,including contact time,p H,adsorbent dose,iron powder dose,initial dye concentration,and temperature.The equilibrium adsorption data were analyzed using three common adsorption models:Langmuir,Freundlich and Temkin.Besides,kinetic and thermodynamic parameters were used to establish the adsorption mechanism.The results showed,in pH =3,contact time = 100 min,ZVI dose = 5000 mg·L~(-1),and MWCNTs dose = 600 mg·L~(-1)in 100 mg·L~(-1)dye concentration,the adsorption efficiency increased to 99.16%.Also,adsorption kinetics was best described by the pseudo-second-order model.Equilibrium data fitted well with the Freundlich isotherm(R2= 0.99).The negative values of ΔG0and the positive value of ΔH0(91.76) indicate that the RR198 adsorption process is spontaneous and endothermic.According to the results,the combination of MWCNTs and ZVI was highly efficient in the removal of azo dyes.     

Adsorption of cationic dyes on Jalshakti®, super absorbent polymer and photocatalytic regeneration of the adsorbent

This paper presents a study on the batch adsorption kinetics of seven cationic dyes, namely, Methylene Blue, Safranine T, Rhodamine B, Crystal Violet, Malachite Green, Brilliant Green, and Basic Fuchsine onto Jalshakti^® (JS), a super absorbent polymer, from aqueous solution. The adsorption of dyes reaches equilibrium in 60–90 min. Equilibrium isotherms and intraparticle diffusion rate constants were measured for single component systems. It is found that uptake of dyes on JS follows the Langmuir and Freundlich isotherm models. The particle diffusion study showed that the initial boundary layer diffusion is followed by intraparticle diffusion effects. The flat and planar dye molecules are readily adsorbed as compared with the propeller shaped triphenylmethane dyes. Photocatalytic regeneration of spent JS using UV/TiO₂ is more effective compared to conventional methods. Further, the regenerated JS exhibits 90% efficiency for subsequent adsorption cycle with Methylene Blue and Safranine T aqueous solutions.     

Adsorption of different dyes from aqueous solution using Si-MCM-41 having very high surface area

Adsorption characteristics of four different dyes Safranin O (cationic), Neutral Red (neutral), Congo Red (anionic) and Reactive Red 2 (anionic) on Si-MCM-41 material having very high surface area are reported. The surface morphology of Si-MCM-41 material before and after adsorbing dye molecules are characterised by FTIR, HRXRD, nitrogen adsorption–desorption isotherms, FESEM, and HRTEM. The adsorption capacities of Si-MCM-41 for the dyes followed a decreasing order of NR > SF > CR > RR2. The adsorption kinetics, isotherm and thermodynamic parameters are investigated in detail for these dyes using calcined Si-MCM-41. The kinetics and isotherm data showed that both SF and NR adsorb more rapidly than CR and RR2, in accordance with pseudo-second-order kinetics model as well as intraparticle diffusion kinetics model and Langmuir adsorption isotherm model respectively. The thermodynamic data suggest that the dye uptake process is spontaneous. The high adsorption capacities of dyes on Si-MCM-41 (q_m = 275.5 mg g^?1 for SF, q_m = 288.2 mg g^?1 for NR) is explained on the basis of electrostatic interactions as well as H-bonding interactions between adsorbent and adsorbate molecules. Good regeneration capacity is another important aspect of the material that makes it potent for the uptake of dyes from aqueous solution.     

Mechanisms of dyes adsorption on titanium oxide– graphene oxide nanocomposites

Graphene oxides (GOs), synthesized with different oxidation degrees and associated with Titanium dioxide (TiO₂) nanoparticles show efficient adsorption processes for dye molecules in solution. The structural, morphology, electronic and optical features of the nanocomposites were investigated by dedicated methods. Water remediation was investigated through the adsorption efficiency of methylene blue (MB) dye as a function of the nanocomposites concentration from 1 to 5 g/L in solutions. While pristine TiO₂ showed a maximum removal of ∼44%, the incorporation of the GO ensures the fast and complete elimination of MB within 9 min. The ball milling process contributed to the increase in the number of defects and surface area in the nanocomposites, which was demonstrated by I_D/I_G ratios by Raman spectroscopy and surface areas by BET. Pseudo-second-order and mechanistic kinetic models were considered, and the performed analysis points out the relevance of the pseudo-second-order model to account for the adsorption kinetics. The Langmuir and Freundlich isotherm models were applied to the experimental data to find an adequate model to describe the adsorption equilibrium, as well as the intra-particle diffusion model during the different adsorption stages involved in the TiO₂/GO nanocomposites. The role of the oxidation degree of GO was clarified through their respective efficiency in the removal of the dyes.     

Photocatalytic Discoloration of Dyes: Relation between Effect of Operating Parameters and Dye Structure

The process of TiO₂/UV photocatalytic discoloration of wastewaters containing organic dyes is influenced by a number of variables. In this paper, the effects of some of these parameters, i.e., mass of catalyst, initial dye concentration, and pH, were related to the structural nature of the dyes investigated, azo and anthraquinone dyes, two families that are representative of about 75 % of the dyes marketed nowadays. Both bibliographical and own experimental data were used to analyze and discuss the photocatalytic discoloration in terms of dye structure and degradation pathways. It is shown that azo dyes (Methyl Orange, Metanil Yellow, Acid Orange 7, and Reactive Red 120) are more easily discolored than Reactive Blue 19 (anthraquinone dye), due to the higher molecular stability of the latter. It is also shown that azo dye discoloration is more influenced by the initial dye concentration, whereas recalcitrant anthraquinone dyes (Reactive Blue 19) mainly demand for basic pH values to generate enough OH^• radicals. Concerning TiO₂ loading, both the bibliographical and current research data showed no effect of this variable in the experimental range analyzed.     

Investigation of Reactive Red Dye 198 removal using multiwall carbon nanotubes in aqueous solution

The present study evaluates the performance of multiwalled carbon nanotubes (MWCNTs) for removing Reactive Red Dye 198 (RR198) from the color wastewater. In this study, the influence of pH, adsorbent dose, initial dye concentration, and contact time on the RR198 adsorption by MWCNTs was investigated. The results showed increasing the dye concentration from 20 to 200 mg/L, removal efficiency decreased from 99.62% to 66.99%. Moreover, by increasing the pH from 3 to 10, the efficiency of dye removal decreased from 76.34% to 54.98%. Freundlich isotherm and pseudo-second-order kinetic model were the best models for describing the adsorption reactions.     

不同结构偶氮染料在TiO2纳米颗粒表面的吸附和光催化降解

为研究不同结构的水溶性偶氮染料在TiO2光催化剂表面的吸附和光催化降解行为,选择4种在印染工业中常用的水溶性偶氮染料：活性红MS、活性蓝B、酸性媒介黑PV和酸性橙156作为研究对象,分别考察在不同pH值和氯化钠存在条件下,TiO2光催化剂对它们的吸附行为和吸附模式,并通过数学模拟方法计算了其在TiO2光催化剂表面的吸附参数,还研究了它们在TiO2光催化剂表面的光催化降解反应. 实验结果表明,4种水溶性偶氮染料在TiO2表面的吸附量随着pH值的升高逐渐降低,而且当pH值处于4~8之间时吸附量下降最为显著. 在相同的吸附条件下,2种酸性染料在TiO2表面的吸附量高于2种活性染料,并且在氯化钠存在下它们的吸附量都得到不同程度的提高. 水溶性偶氮染料的吸附过程符合Langmuir等温吸附模型,活性染料比酸性染料具有更高的吸附平衡常数和覆盖率. 在TiO2对偶氮染料的光催化降解反应中,脱色率和反应速率常数随pH值的升高而降低,并且活性染料比酸性染料更易于发生光催化降解反应.     

Competitive adsorption of Direct Yellow 12 and Reactive Orange 12 on ZnS:Mn nanoparticles loaded on activated carbon as novel adsorbent

A novel adsorbent (ZnS:Mn nanoparticles loaded on activated carbon) was made. The competitive adsorption of Direct Yellow 12 (DY12) and Reactive Orange 12 (RO12) dyes in binary mixture onto this adsorbent was studied. DY12 and RO12 with severe spectra overlapping were chosen and analyzed simultaneously with high accuracy by first order derivative spectrophotometric method in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. Because of the specific characteristics of ZnS:Mn-NP-AC was found to be efficient for the removal of the dyes studied. The adsorption capacities were investigated and described by the mono- and multi-component Langmuir and Freundlich isotherm models for both single and binary dye solutions. The isotherm constants for DY12 and RO12 were calculated. For single solution of DY12 and RO12 dyes, the adsorption capacities of the applied adsorbent were found to be 90.05 mg/g and 94.52 mg/g, respectively. Equilibrium uptake amounts of DY12 and RO12 in binary solution onto the applied adsorbent were found to be considerably decreasing with increasing the concentrations of the other dye. A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. However, at concentrations within moderate ranges, the extended Freundlich isotherm model satisfactorily predicted multi-component adsorption equilibrium data. An endothermic and a spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters.     

Biosorption of a reactive textile dye from aqueous solutions utilizing an agro-waste

In the present study a low-cost waste biomass derived from canned food plant, was tested for its ability to remove reactive textile dye from aqueous solutions. The batch biosorption experiments were carried out at various pH, biosorbent dosage, contact time and temperature. Optimum decolorization was observed at pH 2.0 and 1.6 g dm^− 3 of biomass dosage within 20 min. The first-order and the pseudo-second-order kinetics were investigated for the biosorption system. The applicability of the Langmuir and Freundlich isotherm models was examined. The thermodynamic parameters for the biosorption were also calculated. The experimental results in this study indicated that this low-cost biomaterial was an attractive candidate for the removal of textile dye Reactive Red 198 (RR198) from aqueous solutions.     

Photoassisted hetero-Fenton mineralisation of azo dyes by Fe(II)-Al2O3 catalyst

Photoassisted Fenton mineralisation of two azo dyes Direct Red 23 (DR 23) and Reactive Orange 4 (RO 4) was studied in detail using a Fe(II) loaded Al₂O₃ as a heterogeneous catalyst in presence of H₂O₂ and UV-A light. 25 and 15% FeSO₄ loaded Al₂O₃ show the maximum efficiency in the degradation of DR 23 and RO 4 respectively. The effects of catalyst loading, H₂O₂ concentration, initial solution pH and initial dye concentration on photodegradation were investigated and the optimum conditions are reported. DR 23 undergoes easy degradation when compared to RO 4. The difference is due to the presence of stable triazine ring system in RO 4. The catalyst is reusable and the leaching of Fe(II) from the catalyst in each run is less than 10% in the pH range 2–7.