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Toxic heavy metals As(V) and Cr(VI) removal from water environment has becoming more and more urgent due to their adverse health effect. In this study, the flowerlike Ce/Fe bimetallic oxides (CFBO), which combined the superiority of three-dimensionally (3D) hierarchical architectures and bimetallic synergistic effect, were innovatively designed and synthesized via one-step facile template-free hydrothermal method. Compared with pure iron oxides (PIO), the obtained CFBO exhibited excellent performance for As(V) and Cr(VI) removal, and the maximum adsorption capacities toward As(V) and Cr(VI) increased from 49.09 mg/g to 164.94 mg/g and 38.07 mg/g to 127.42 mg/g, respectively. Both As(V) and Cr(VI) removal efficiency decreased with an increasing solution pH due to the pHzpc of CFBO, but exhibited slightly change with coexisting anions except for SiO32− and PO43− ions. Combined results of FT-IR and XPS, it was concluded that the abundant hydroxyl groups existed on the surface of CFBO played a key role in the high uptake of As(V) and Cr(VI), and subsequently formed inner-sphere surface complexes. Attractively, the remarkable removal efficiency of As(V)/Cr(VI) in column experiments revealed that the CFBO had great potential for practical application.

The widespread occurrence of penicillin antibiotics (PENs) in natural environment has raised increasing concerns due to their potential to induce antibiotic-genes. In this study, the degradation of PENs by UV/peroxodisulfate (PDS) process was investigated to determine the reaction kinetics, transformation mechanism and energy efficiency. The second-order rate constants for sulfate radical (SO4− ) and hydroxyl radical (HO ) with PENs, including, pencillin G (PG), amoxicillin (AMX) and carbenicillin (CBN), were determined to be (3.90–9.32) × 109 M−1·s−1 and (6.67–9.86) × 109 M−1·s−1, respectively. A pseudo steady-state kinetic model was employed and successfully predicted the degradation of PENs in ultrapure water. The modeling results revealed that both direct and indirect photolysis contributed to PENs degradation, and the contribution of indirect photolysis increased with the increase of PDS dosage. SO4− was the major contributor to PENs indirect photolysis. The effect of pH and water matrices, including HCO3−, Cl− and natural organic matter were evaluated and modeled. Combined with the modeling results, the derived radicals and excited species were likely generated and involved in the overall degradation of PENs. Based on the developed model, we gave a roughly calculation of electrical energy per order (EE/O) to evaluate the energy efficiency of PDS treatment processes. Finally, the transformation product analysis indicated that the thioether sulfur on the five-membered ring and the side chain, e.g., benzene ring on PG and CBN were the reactive sites for SO4− , while the primary amine was another reactive site for SO4− on AMX.

Microalgae play an important role in carbon sequestration by converting solar energy into biomass as an energy reserve. The conversion efficiency is often limited by light absorbed in the chloroplast. It is of great potential to enhance the photosynthesis capability by improving susceptibility of the light absorption by microalgae. Carbon-based quantum dots (QDs) are promising candidates for spectrum conversion, exhibiting remarkable biocompatibility, excellent water solubility, and customizable flexibility. Herein, we introduced graphene oxide quantum dots (GOQDs) with a blue light (465 nm) emission after ultraviolet (380 nm) excitation into the microalgae growth media. It is demonstrated that the ultraviolet light was effectively absorbed and utilized by the chlorophyll in the GOQDs-Chlorella pyrenoidosa system, resulting in a significantly increased photosynthetic activity. Moreover, a 20% improvement in carbon dioxide fixation and a 34% increase in bioenergy accumulation was found in the system. We further examined the microalgae metabolic pathways to reveal the biological response mechanism with GOQDs. Results verified that the GOQDs facilitated photosystem II (PSII) energy transfer to improve the photosynthesis of microalgae and upregulated the metabolites of lipid biosynthesis, resulting in a higher biomass and lipid content. This work suggested that using GOQDs as a promising approach for to improve the photosynthetic efficiency of microalgae, as well as a great potential for enhancing carbon capture and bioenergy production, especially in the environments with higher solar ultraviolet irradiation.

The occurrence of tetracycline (TTC) in the environment can exacerbate microbial selection pressure and trigger bacterial resistance, raising potential risks to the ecosystem and public health. Here, we report that copper supported polyurethane foam (Cu-NC) can efficiently activate PMS to degrade TTC. Results demonstrated that the degradation rate of TTC was 91.3% and the pseudo first-order kinetic constant of 0.0762 min−1 was achieved after 40 min reaction at pH 5.0. Activation of PMS by Cu-NC was proposed to proceed via two sequential processes, which was different from the conventional mechanism for sulfate radical generation. Cu0 initially reacts with dissolved oxygen to generate H2O2 and Cu(I)(s) in situ in the solid form. Then Cu(I)(s) solves the relative instability of low-valent transition metal ions in aqueous solution, thus improving the activation efficiency of PMS. A novel mechanism for Cu(I)(s) activation of PMS to generate HO• was proposed and elucidated through outer-sphere interaction (electrostatic bonding) and acid-base theory. Superoxide radical and Cu0 accelerate the Cu(II)/Cu(I) redox, overcoming the rate-limiting step in Fenton-like reaction. Cu-NC showed an excellent cycling stability (80.8% removal efficiency after fifth run) in PMS activation with low Cu ion leaching (＜0.2 mg/L). The Cu-NC/PMS system also exhibited satisfactory removal of TTC in the presence of various water matrices. This study can deepen the understanding of the generation of HO• in the PMS activation process and provide a promising strategy for pollutants degradation in wastewater treatment.

Inorganic arsenic cycling in the natural environment is significantly controlled by manganese/iron oxides, and studying the redox transformation of arsenic in both aqueous and solid phase is therefore essential to understand its environmental toxicity and predict its environmental behavior. Herein, the synthesized magnetic thin-film MnO 2 nanosheet-coated flowerlike Fe 3 O 4 nanocomposites have been used to simultaneously investigate the potential redox transformation of arsenic in aqueous phase and arsenic speciation on the solid phase interface. The results showed the initial Mn/Fe ratio has serious influenced the morphologies, textural properties and uptake of arsenic in aqueous solution. The maximum adsorption capacities of As(III) and As(V) by MF2 were 76.73 mg/g and 120.50 mg/g, respectively. After 10 h reaction, the total arsenic concentration in both As(III)-MF2 system and As(V)-MF2 system far below than that of 10 μg/L, which was setted the maximum guideline concentration value in drinking water by World Health Organization (WHO). HPLC-ICP-MS revealed that in aqueous solution part of As(III) was oxidized into As(V), while As(V) was not reduced into As(III). X-ray absorption near edge structure (XANES) and XPS analysis from solid phase further confirmed that the MnO 2 nanosheet mainly acted as an oxidant, while flowerlike Fe 3 O 4 only played the role as an arsenic species adsorbent. Extended X-ray absorption fine structure (EXAFS) analysis indicated that both As(III) and As(V) formed inner-sphere bidentate binuclear corner-sharing ( 2 C ) complexes with an As-Fe interatomic distance of 3.32–3.34 A on the interface of As-MF2 solid phase.

Coking wastewater (CWW) is one of the most challenging industrial wastewaters to treat, due to its complex chemical composition, high organic load, and potential toxicity to human and environmental health. A full-scale coking wastewater treatment plant with a two-stage anoxic-oxic-anoxic-oxic (A1/O1/A2/O2) process was investigated systematically. The experimental results showed that the AOAO process exhibited an excellent removal capacity of COD, ammonia, nitrate, and total nitrogen. The GC × GC-TOF MS analysis investigated that the majority of refractory organic compounds, such as phenols, quinolines, polycyclic aromatic hydrocarbons, hydrocarbons, etc., were either fully decomposed or exhibited significant decreases in concentration during the full-scale AOAO process, which offered insights to the biodegradation dynamics of CWW organic components. Microbial community analysis showed that bacterial communities were remarkably altered in the four bioreactors of the AOAO process: Proteobacteria dominated during the whole AOAO process, while Nitrospirae and Bacteroidetes enriched in the primary and secondary AO process, respectively. Moreover, metagenomic sequencing found that the relative abundances of amino acid metabolism and carbohydrate metabolism in the primary AO process were both higher than that in the secondary AO process. It indicated that as the AOAO process progressed, the changes in operational characteristics could remarkably affect the variations of functional microorganisms responsible for organics and nitrogen removal and metabolic functions of microbial community. Through this study, a comprehensive assessment of the AOAO biological processes of coking wastewater treatment was achieved, which provided valuable insights to the operation and evaluation of relevant real treatment plants.

While peracetic acid (PAA) are known to be susceptible to decomposition by metals for radical generation, herein we report a novel decomposition process of PAA with TiO2 nanoparticle (nTiO2) for the first time. nTiO2 in anatase (A_nTiO2) could significantly enhance the decomposition of PAA, whereas, nTiO2 in rutile phase had no impact on the stability of PAA. Electron paramagnetic resonance (EPR) technique and a radical quenching study indicated lack of involvement of reactive radicals. In-depth investigation revealed that the {0 0 1} facets of A_nTiO2 with high surface free energy were especially reactive for the catalytic decomposition of PAA. Theoretical calculations proved the adsorption of PAA onto A_nTiO2 {0 0 1} surface was much more favorable than the predominated {1 0 1} facets. The unsaturated five coordinated Ti (Ti5c), typical Lewis acid sites on A_nTiO2 {0 0 1} surface, were further confirmed as the dominant active sites for catalyzing PAA decomposition. This novel decomposition process could enhance the stability and migration of A_nTiO2, increasing the potential environmental risk. Meanwhile, the disinfection of PAA was inhibited by introducing A_nTiO2. The new findings of this study broaden the knowledge on PAA decomposition process, and have an important implication for PAA disinfection and environmental behavior of TiO2 nanoparticle.

The potential performance of thermally activated persulfate (TAP) oxidation on the degradation of Triclosan (TCS), a widely used antibacterial agent, was investigated under different conditions. TCS degradation by TAP oxidation was found to fit well with an Arrhenius behavior from 50 to 80 °C, yielding apparent activation energy 121.12 kJ/mol. TCS removal was found to be pH-dependent. Acidic conditions (pH 3–5) were beneficial to TCS removal. The performance of TAP oxidation was still promising under circumneutral pH value (pH ∼7). The presence of alkaline species (with concentrations ranging from 1 to 50 mM) presented inhibitory effects on TCS degradation. When concentration of fulvic acid (FA) in solution increased to 10 mg/L, the effect on TCS degradation became increasingly negative. Different with alkaline species and FA, chloride ions at relatively low ( 10 mM) and high (20–50 mM) concentrations exhibited dual effects on TCS degradation. Both sulfate radicals and hydroxyl radicals were confirmed in the system by Electron Paramagnetic Resonance spectra, and the quenching study indicated that sulfate radicals were the predominant oxidants responsible for the TCS degradation. The major intermediate derived from TCS degradation was identified to be 2,4-dichlorophenol and the reaction scheme was proposed. Additionally, the ecotoxicity of TCS and its degraded samples was assessed by a 4-day zebrafish embryo-larval bioassay, which indicated the capacity of thermally activated persulfate oxidation to decrease ecotoxicity, thus confirmed the sulfate radicals based oxidation a promising alternative of in situ chemical oxidation from the environmental risk standpoint.

The influence of a biodegradable agent, N,N-bis(carboxymethyl)glutamic acid (GLDA), on chloramphenicol (CAP) degradation in pyrite/H2O2 system was investigated. The results indicated that the presence of GLDA could extend the working pH range and provided favorable performance at alkaline conditions. The addition of 100 μmol/L GLDA increased the CAP removal rate to 83.3% at pH 8 due to the reinforced formation of OH. The beneficial effect was found to be indifferent of possible reduction of redox potential (Fe(III)/Fe(II)), probable decrease of reaction pH and complex of structured iron on pyrite surface. However, it was correlated well with the facilitated autocatalytic oxidation reaction by Fe(III)-GLDA that promoted cycle of iron, which was confirmed by the determination of ESR and sulfate ion leaching. Based on GC–MS results, the presence of GLDA led to further oxidation of product with reinforced oxidation efficiency, and the potential degradation routine remains similar. All these provide some fundamental insights into the characteristics of environment friendly GLDA-enhanced pyrite/H2O2 system for bio-refractory contaminants removal under neutral or alkaline conditions, and enrich the theoretical knowledge of heterogeneous Fenton-like processes.

It is necessary to explore the best treatment to eradicate trimethylamine [TMA] in air, since it is toxic and hazardous to the living organism. Photocatalysis, a low-cost and environmentally friendly technology, has been studied in comparison with photo-electrochemical catalysis in the removal of TMA gas. In this study, it is most quickly and efficiently degraded using Co-MoS2 composite catalyst in an integrated system of (PEC) photo-electrochemical catalysis. The performance of the catalyst and system was evaluated by TMA removal ratio. As a result, the catalyst has good degradation performance for TMA in the PEC system, which indicates that it has high photocatalytic activity and high apparent quantum efficiency. In addition, the stability of the Co-MoS2 catalyst in the PEC is better than in PC due to the presence of the external bias generated by the assisted electrochemistry in the PEC system.

Advanced oxidation processes (AOPs) always rely on the generation of inorganic radicals (e.g., HO ) for contaminant destruction. Herein, we report a novel AOP, i.e., Co3O4/peracetic acid (PAA) to degrade contaminants with organic radicals at neutral pH. Using orange G (OG) as a representative, studies show that Co3O4 can effectively activate PAA to promote rapid degradation of OG at neutral pH, with extremely low cobalt leaching. Moreover, Co3O4 exhibits high structural and chemical stability in PAA activation. X-ray photoelectron spectroscopy (XPS) analysis indicated the recycling of Co2+/Co3+, and thus confirmed a catalyst role of Co3O4 in the activation of PAA. Electron paramagnetic resonance (EPR) technique and radical-quenching studies showed that organic radical species, (i.e., CH3C( O)O and CH3C( O)OO ) played a critical role in the degradation process. A wide range of contaminants were further tested for their degradation in the PAA/Co3O4 system, and this system was found to exhibit certain selectivity for organic contaminants, especially for those with electron-rich functional groups/moieties, e.g., fluoroquinolones and sulfonamides. This work provides a promising strategy for the degradation of organic contaminants in water treatment.

Toxic arsenic species cycle in the geochemical process are strongly influenced by iron and manganese elements, thus understanding mutual transformation of multiple Fe/Mn redox states is essential to predict the redox transformation and sequestration of arsenic in natural environment. Herein, a nanosized magnetic mesoporous iron manganese bimetal oxides (Nanosized-MMIM) with highly well-ordered inner-connected structure and large surface area was fabricated, the obtained Nanosized-MMIM possessed higher content of surface-bound Fe(II) than Commercial Fe3O4 and Templated Fe3O4 due to the difference of standard redox potential of multiple Fe(II-III)-Mn(II-III) valence states and the synergistic effect of Fe-Mn bimetal oxides. This structural surface-bound Fe(II) was greatly associated to the OHads radicals that generated from the interface catalysis of materials via the Fenton-like pathway. The potential redox transformation of arsenic in liquid-solid two phase by using HPLC-ICP-MS and XPS investigation indicated that As(III) in water was mainly oxidized into As(V) by bulk solution OHfree radicals (30.39%) and surface-bound OHads radicals (69.16%), then the generated As(V) was subsequently adsorbed on the Nanosized-MMIM surface. This study could further improve the deeply understanding on the As(III) abiotic oxidation and sequestration in Fe-Mn co-existed natural environment such as minerals, soils and sediments.

The extensive use of cephalosporin antibiotics (CEFs) leads to the frequent detection of CEFs in different aquatic matrices. Sulfate radical based advanced oxidation processes are efficient in eliminating CEFs. However, the efficiency of CEFs degradation in elevated salt concentration and the transformation products, as well as the corresponding toxicity are still unknown. In this study, CEFs degradation by thermally activated persulfate (PS) in various matrix components were investigated systematically. CEFs degradation could be promoted in Cl− and HCO3− containing matrices, while the mixed matrices of NOM with salt could have an inhibitory effect on CEFs degradation. SO4 −, OH and chlorine radicals were identified to contribute to CEFs transformation in the presence of Cl−. Based on the pseudo-steady kinetic modeling, the contribution of chlorine radicals was estimated to be >90% as Cl− concentration increased to 50 mM. CO3 − was the predominant radical for CEFs degradation in the HCO3− containing matrix. However, the contribution of CO3 − was much less than chlorine radicals, and 70–80% of CEFs degradation was ascribed to CO3 − at HCO3− concentration of 500 mM. The same major products were identified in non-matrix and matrix containing systems, but the products concentration and the evolution rate were enhanced in matrix containing systems. The acute toxicity assay demonstrated that the toxicity of CEFs solution was reduced by thermally activated PS in both non-matrix and matrix containing systems. Compared with surface water and wastewater, CEFs degradation was promoted in high salt containing hospital wastewater, suggesting that thermally activated PS is a promising approach to treat antibiotics in high salinity wastewater.

Calcium peroxide (CP) combined persulfate (PS) oxidation is an emerging in situ chemical oxidation (ISCO) technology for ground water remediation. Many field cases also confirm its effectiveness in ground water remediation while few research articles document it. This study investigated the performance of α-methylnaphthalene (MN) degradation by PS/CP to further understand this dual oxidant application in ISCO. Results showed that MN could be completely oxidized in 72 h with 1 g L −1 PS and 1 g L −1 CP. The degradation rates of MN increased with the increase of PS and CP concentration. MN degradation was significantly enhanced with the solution pH decrease, because CP was easier to dissolve and generated more radicals in acidic condition. Solutes in ground water including chloride ions, alkalinity and natural organic matters presented inhibitory effect on MN degradation in this dual oxidant system. Plausible mechanisms of the sulfate and hydroxyl radicals in the system were proposed based on the results of radical scavenging experiments and electron spin resonance (ESR) tests. It appeared that surface OH of CP was also responsible for the MN removal. The major oxidation products in this study were 1-naphthaldehdye, naphthalene-1-ylmethanol and 4-hydroxy-4-methylnaphthalen-1(4H)-one. To better understand PS/CP in ISCO, the degradation of MN was tested in ground water matrix, which showed satisfactory efficiency. The results of this study provided some detail information of PS/CP dual oxidant in degradation organic contaminants, which might provide some references for the application of this technology in ISCO.

Cotton-like Ca–Al–La composite as an adsorbent for fluoride removal was successfully synthesized by an easy one-step hydrothermal process. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the samples have uniform and cotton-like morphology. Batch sorption experiments were conducted to study the influence of various factors such as pH, initial fluoride concentration, equilibrium contact time, co-existing anions on the sorption of fluoride. The fluoride adsorption over the Ca–Al–La composite follows the Langmuir model. The maximum adsorption capacity of the adsorbent is 29.30 mg/g. The fluoride adsorption kinetics over the adsorbent can be well described by the pseudo-second-order kinetic model. In addition, the cotton-like Ca–Al–La composite showed high fluoride removal efficiency over a wide range of pH (3–11).

Due to the limitations such as sludge formation and early termination exist in the classic Fenton reaction, an enhanced Fenton system catalyzed by heterogeneous pyrite was used to degrade nitrobenzene in this study. The results demonstrated that the degradation of nitrobenzene by the pyrite Fenton system (80%) was significantly enhanced compared to that demonstrated by a classic Fenton system. The appropriate Fe(II) concentration generated by constant dissolution from a pyrite surface and by recycling Fe(III) contributed to this enhancement. The degradation of nitrobenzene in the pyrite Fenton reaction can be properly described by pseudo-first-order kinetics, whereas that in the classic Fenton system exhibited an early termination of the nitrobenzene degradation. The degradation kinetics of nitrobenzene in the pyrite Fenton reaction was obviously influenced by the concentrations of pyrite, H2O2 and nitrobenzene. However, no obvious effect of the initial pH on the degradation kinetics of nitrobenzene was observed in the pyrite Fenton reaction due to the production of hydrogen accompanied by aqueous Fe(II) generation. Degradation of the nitrobenzene was obviously inhibited by the addition of t-butanol (OH scavenger), suggesting that nitrobenzene was dominantly oxidized by HO generated in the pyrite Fenton system. Phenol, 2-nitrophenol, 3-nitrophenol and 4-nitrophenol were the major transformation products detected in the system, due to the attack of hydroxyl radicals to the aromatic ring and nitro group of nitrobenzene.

Nanoscale zero-valent iron (nZVI) for removal of cadmium from polluted water was investigated. Batch experiments were conducted at 1:100 mass ratio of Cd to nZVI to investigate low, medium and high concentration levels of species. Effect of solution pH was importantly evaluated on the removal efficiency of Cd(II) by nZVI. The removal process is fast and can reach equilibrium in less than 30 min. The cadmium removal efficiency increases rapidly with rising pH in the range of 3.0–8.6, maximum removal capacity of 66.9 mg Cd(II)/g nZVI was observed. Benchmark tests were also conducted with oxidized nZVI (nZVI oxidized with oxygen bubbling), which had much lower removal efficiency of Cd(II) under identical conditions. Flow experiments with a two-stage reactor were performed to examine the effects of hydraulic retention time, influent cadmium concentration, nZVI recycle ratio and nZVI dose. Removal efficiency over 91% was achieved within a residence time of 20 min in a two-stage flow reactor. Higher nZVI recycle ratio and longer hydraulic retention time enhanced removal efficiency. Transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray powder diffraction were employed to characterize nZVI before and after the reactions. Data suggest that Cd(II) is sequestrated within nZVI by adsorption or surface complex formation with no apparent reduction of Cd(II).

A novel multi-templates molecularly imprinted polymer (MIP), using acidic pharmaceuticals mixture (ibuprofen (IBP), naproxen (NPX), ketoprofen (KEP), diclofenac (DFC), and clofibric acid (CA)) as the template, was prepared for the removal of acidic pharmaceuticals from contaminated water. The sorption behaviors of the MIP including sorption kinetics, isotherms, effect of pH and ionic strength were investigated in detail. The MIP exhibited excellent selectivity affinity toward five acidic pharmaceuticals with higher binding capacity in water compared to non-imprinted polymer (NIP). The pseudo-second-order model well described the adsorption of acidic pharmaceuticals on the MIP. The feasibility of applying MIP for removing acidic pharmaceuticals from contaminated environmental water was demonstrated by comparing the adsorption capacity of acidic pharmaceuticals in spiked lake water to that in deionized water. In addition, the MIP could be used at least fifteenth cycles without obvious loss in adsorption capacity.

Bamboo charcoal-based, iron-containing adsorbent (Fe–BC) was developed by using bamboo charcoal (BC) as a supporting medium for ferric iron that was impregnated by Fe 2 (SO 4 ) 3 and H 2 SO 4 simultaneous treatment, followed by microwave heating. The low-cost composite was characterized and used as an adsorbent for Cr(VI) removal from water. The results showed that the BET specific surface area, total pore volume, and average mesoporous diameter of Fe–BC all decreased with iron impregnation. As an adsorbent, Fe–BC showed an excellent adsorption capability for Cr(VI), the adsorption process followed the Langmuir model, and the adsorption kinetic followed pseudo-second-order model. The adsorption of Cr(VI) onto Fe–BC was spontaneous and exothermic under the studied conditions. Column adsorption experiment with Fe–BC showed that Cr(VI) could be removed to below 0.05 mg/L within 360 bed volumes at empty bed contact time 2 min when the groundwater containing approximately 0.12 mg/L of Cr(VI) was treated. The spent Fe–BC adsorbent could be readily regenerated for reuse by dilute NaOH solution.

a b s t r a c t The TiO2/sepiolite composites were successfully prepared by a facile and low-cost sol-gel technique at low temperature, using TiCl4 as a precursor. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectrum (UV-vis DRS), N2 adsorption-desorption and Fourier trans- form infrared (FT-IR) spectroscopy. The results showed that the ordered structure of sepiolite in the as-prepared samples was destroyed to some extent and the particle sizes of TiO2 in the composites were less than 10 nm. The as-prepared samples showed an efficient photocatalytic activity for the degradation of acid red G (ARG) and 4-nitrophenol (4-NP) under UV light irradiation, which could be attributed to the synergetic effect of the large specific surface area of the TiO2/sepiolite composites and the anatase phase of TiO2 in it. © 2010 Elsevier B.V. All rights reserved.

We successfully synthesized the TiO 2 /kaolinite (TiO 2 /Kao) composites with mixed phase TiO 2 using a simple method at low temperature. The as-prepared TiO 2 /Kao composites were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption/desorption measurements, Fourier transform infrared (FT-IR) spectroscopy and UV–vis diffuse reflectance spectra (DRS). The X-ray diffraction analysis indicated that the binary mixtures of anatase and rutile or the binary mixtures of anatase and brookite or the ternary mixtures of anatase, brookite, and rutile exist in the TiO 2 /Kao composites. The specific surface area of the TiO 2 /Kao composites is much higher than that of the kaolinite. The as-prepared samples exhibited strong photocatalytic activity for the removal of acid red G (ARG) and 4-nitrophenol (4-NP). The composites obtained at 70 °C showed the highest photocatalytic activity, in which the mixed phases of anatase and brookite existed. The high specific surface area and heterojunction microstructure could be responsible for the high photocatalytic activity.