Enhanced photocatalytic degradation of dye pollutants under visible irradiation on Al(III)-modified TiO2: structure, interaction, and interfacial electron transfer

Aluminum(III)-modified TiO2 was prepared by sol-gel process via a sudden gelating method. The structure of the modified material and the local environment of aluminum were investigated using X-ray diffraction, HRTEM, XPS, 27Al MAS NMR, and xi-potential measurements. The effect of the aluminum modification on interaction between the dye and photocatalyst, the interfacial electron transfer process, and thereby the degradation of dye pollutants under visible irradiation were also examined by FTIR spectra and UV-vis diffuse reflectance spectra. It was found that, rather than incorporating into the crystal lattice of TiO2, the aluminum forms an overlayer of Al2O3 on the surface of TiO2, interfaced with Ti-O-Al bonds. It is interesting that the carboxylate-containing dyes such as Rhodamine B (RhB) adsorb preferentially on the Al2O3, rather than the Ti(IV) sites on the surface of TiO2. The photodegradation rate observed for RhB is nearly 5-fold faster than that obtained in the pristine TiO2 system. The photodegradation of dyes on the aluminum(III)-modified photocatalyst is of great dependence on the structure and anchoring group of the dyes. Structure with carboxylate as anchoring group and amino group as electron donor is favorable for degradation. The mechanistic details are discussed on the basis of experimental results.     

Environmental remediation by an integrated microwave/UV illumination method. V. Thermal and nonthermal effects of microwave radiation on the photocatalyst and on the photodegradation of rhodamine-B under UV/Vis radiation

The photocatalyzed degradation (PD) of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using UV/Vis illumination assisted by microwave radiation (PD/MW). The initial degradation by the PD/MW method is compared to the PD method and to the thermally assisted PD method using conventional heating (PD/TH). Total organic carbon (TOC) assays show that the efficiency of complete mineralization of the dye follows PD/MW > PD/TH > PD > MW. In all cases, microwave radiation alone had no effect on the loss of TOC. The degradation involving microwave radiation was especially efficient when coupled to UV irradiation. By contrast, the extent of degradation of RhB involving suitable excited states through visible irradiation of the dye was rather inefficient when coupled to microwave radiation. Contact angle measurements on the TiO2 photocatalyst particles indicate that microwave radiation also causes an increase in the hydrophobic character of the TiO2 surface, with consequences on the adsorption mode of the dye substrate and thus on the overall mechanism of degradation. Deethylated RhB intermediates were identified by an electrospray ESI ionization mass spectral technique in the positive ion mode and subsequently confirmed by HPLC/absorption spectroscopy. Computer simulations led to estimates of frontier electron densities of all atoms of the RhB structure, affording inferences as to the position of radical attack on RhB. The nitrogen atoms of the dye were all converted to NH4+ ions. The major difference between the thermally assisted PD/TH method and the microwave-assisted PD/MW method showed that nonthermal effects from the microwave radiation impact significantly on the nature of the photocatalyst surface. These effects led to a more efficient photodegradation and mineralization of the dye substrate.     

纳米TiO2光催化氧化处理直接耐晒翠蓝染色废液

采用纳米级TiO2悬浮法光催化氧化处理直接耐晒翠蓝染液，讨论pH值、催化剂用量、染料浓度和脱色时间等因素对脱色与降解的影响。试验发现，纳米TiO2对染料的脱色效率高，降解彻底，是一种很有前途的印染废水处理方法。     

Degradation of dye pollutants by immobilized polyoxometalate with H2O2 under visible-light irradiation

A Keggin polyoxometalate (POM, i.e., PW12O40(3-)) and its lacunary derivative are immobilized on an anionic exchange resin through electrostatic interaction at pH 4.6 in an aqueous dispersion. The resin-supported POM thus obtained catalyzes the efficient degradation of cationic dye pollutants in the presence of H2O2 under visible-light irradiation. To evaluate the photocatalytic system, degradation of a rhodamine B (RB) dye was investigated in detail using UV-visible spectroscopy, high performance liquid chromatography, and gas chromatography/mass spectrometry techniques to identify the intermediates and final products. Fluorescence lifetime measurements revealed the electron transfer from the visible-light-excited RB molecules to the POMs. Electron paramagnetic resonance measurements, investigation of the effects of *OH and *OOH scavengers on the photoreaction kinetics, and IR analysis indicated that de-ethylation of RB was due to *OOH radicals, but the decomposition of the conjugated xanthene structure was caused by the peroxo species formed by interaction of H2O2 with the lacunary POM loaded on the resin. A total organic carbon removal of ca. 22% was achieved, and the recycle experiment suggested excellent stability and reusability of the heterogeneous catalyst. On the basis of the experimental results, a photocatalytic mechanism is discussed.     

Decomposition of environmentally persistent trifluoroacetic acid to fluoride ions by a homogeneous photocatalyst in water

Decomposition of trifluoroacetic acid (TFA) was achieved with a tungstic heteropolyacid photocatalyst H3PW12O40*6H2O in order to develop a technique for measures against TFA stationary sources. This is the first example of C-F bond cleavage in an environmentally harmful perfluoromethyl-group-containing compound using a homogeneous photocatalyst. The catalytic reaction proceeds in water at room temperature under UV-visible light irradiation in the presence of oxygen. The system produces only F- ions and CO2; the (mole of formed F-)/(mole of decomposed TFA) and (mole of formed CO2)/(mole of decomposed TFA) ratios were 2.91 and 2.09, respectively. GC/MS measurements showed no trace of other species such as environmentally undesirable CF4, which is the most stable perfluorocarbon and has a very high global warming potential. When the (initial TFA)/(initial catalyst) molar ratio was 20:1, the turnover number of TFA decomposition reached 5.58 by 72 h of irradiation, accompanying with no catalyst degradation. The catalytic reaction mechanism can be explained by a redox reaction between the catalyst and TFA, involving a photo-Kolbe process.     

Synergetic effect of Bi2WO6 photocatalyst with C60 and enhanced photoactivity under visible irradiation

Fullerene (C60)-modified Bi2WO6 photocatalyst is prepared by a simple absorbing process. The as-prepared samples show the high efficiency for the degradation of nonbiodegradable azodyes methylene blue (MB) and rhodamine B (RhB) under visible light (lamda >420 nm) and simulated solar light (lamda >290 nm). After being modified by C60, the photocatalytic activities of Bi2WO6 samples increase about 5.0 and 1.5 times for the degradation of MB and RhB under visible light irradiation, whereas 4.6 and 2.1 times under xenon lamp irradiation, respectively. The enhanced photocatalytic activity for C60-modified Bi2WO6 comes from the high migration efficiency of photoinduced electrons on the interface of C60 and Bi2WO6 which is produced by the interaction of Bi2WO6 and C60 with the conjugative pi-system. The optimum synergetic effect is found at a weight ratio of 1.25 wt % (C60/Bi2WO6). The photocatalytic reaction process of C60-modified Bi2WO6 is mainly governed by direct holes and O2*- oxidation.     

Semiconductor-mediated Photocatalyzed degradation of a herbicide derivative, chlorotoluron, in aqueous suspensions

The photocatalytic degradation of a herbicide derivative, chlorotoluron [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 1], has been investigated in aqueous suspensions of titanium dioxide (TiO2) under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis technique and depletion in total organic carbon (TOC) content as a function of irradiation time. The degradation kinetics of the model compound was investigated under different conditions such as type of TiO2, pH, catalyst concentration, substrate concentration, temperature, and in the presence of different electron acceptors such as hydrogen peroxide (H2O2), potassium persulfate (K2S2O8), and potassium bromate (KBrO3) besides molecular oxygen. TiO2 Degussa P25 was found to be a more efficient photocatalyst for the degradation of the model compound as compared with other photocatalysts. The degradation products were analyzed using GC/MS analysis technique and probable pathways for the formation of different products have been proposed.     

Simultaneous and synergistic conversion of dyes and heavy metal ions in aqueous TiO2 suspensions under visible-light illumination

This study reports synergistic effects in the simultaneous conversion of dyes and heavy metal ions in aqueous TiO2/dye/metal ion systems (ternary components) under visible light (lambda > 420 nm). TiO2/Cr(VI)/Acid Orange 7 (AO7), TiO2/Cr(VI)/Rhodamine B (RhB), TiO2/Ag+/AO7, and TiO2/Ag+/RhB were chosen as test systems. Although dyes can be degraded in TiO2 suspensions under visible light, their removal rates were markedly enhanced in the presence of metal ions. Similarly, the reduction rates of metal ions in visible-light-illuminated TiO2 suspensions were negligible, but they were highly accelerated with dyes present. In particular, the synergistic effect in the ternary system of TiO2/Cr(VI)/AO7 was outstanding. The presence of dissolved oxygen increased the photoreduction rate of Cr(VI) despite the fact that Cr(VI) and O2 are competing electron acceptors. This is ascribed to in-situ photogenerated H2O2 from O2, which acts as a reductant of Cr(VI). RhB and Ag+ ions could be also converted simultaneously under visible light both in the presence and absence of TiO2. The visible-light-induced reduction of Ag+ did not occur at all in TiO2/Ag+ system, but it was enabled in both TiO2/Ag+/ RhB and TiO2/Ag+/AO7 to generate Ag particles. On the other hand, the binary systems of Cr(VI)/AO7, Ag+/AO7, and Ag+/RhB show significant visible-light activities for the conversion of both dye and metal ion. In this case, metal ions and dyes seem to form complexes that induce intracomplex electron transfers upon visible-light absorption. The Cr(VI)/RhB system, however, exhibited insignificant visible-light reactivity.     

Degradation of cationic red GTL by catalytic wet air oxidation over Mo-Zn-Al-O catalyst under room temperature and atmospheric pressure

To overcome the drawback of catalytic wet air oxidation (CWAO) with high temperature and high pressure, the catalytic activity of Mo-Zn-Al-O catalyst for degradation of cationic red GTL under room temperature and atmospheric pressure was investigated. Mo-Zn-Al-O catalyst was prepared by coprecipitation and impregnation. XRD, TG-DTG, and XPS were used to characterize the resulting sample. Central composition design using response surface methodology was employed to optimize correlation of factors on the decolorization of cationic red GTL. The results show that the optimal conditions of pH value, initial concentration of dye and catalyst dosage were found to be 4.0, 85 mg/L and 2.72 g/L, respectively, for maximum decolorization of 80.1% and TOC removal of 50.9%. Furthermore, the reaction on the Mo-Zn-Al-O catalyst and degradation mechanism of cationic red GTL was studied by Electron spin resonance (ESR) and GC-MS technique. The possible reaction mechanism was that the Mo-Zn-Al-O catalyst can efficiently react with adsorbed oxygen/H(2)O to produce ·OH and (1)O(2) and finally induce the degradation of cationic red GTL. GC-MS analysis of the degradation products indicates that cationic red GTL was initiated by the cleavage of -N ═ N- and the intermediates were further oxidized by ·OH or (1)O(2).     

Catalyzed degradation of azo dyes under ambient conditions

Phase-pure layered perovskite La(4)Ni(3)O(10) powders were synthesized by a solution combustion approach. It is found that, in the presence of the La(4)Ni(3)O(10) powders, aqueous azo dyes can be degraded catalytically and efficiently under ambient conditions. Neither light nor additional reagents are needed in the catalytic reaction. The dye degradation procedure can be accelerated markedly by magnetic stirring. A systemic series of chemical and electrochemical experiments suggested that the dye degradation proceeds through electron transfers from the dye molecules to the catalyst and then to electron acceptors such as dissolved oxygen. The present catalytic degradation requires no additional reagents or external energy input, which hence provides a potentially low-cost alternative for the remediation of azo-dye effluents.     

Synergetic degradation of rhodamine B at a porous ZnWO4 film electrode by combined electro-oxidation and photocatalysis

Synergetic degradation of rhodamine B (RhB) was investigated by combining electro-oxidation and photocatalysis using porous ZnWO4 film at various bias potentials. The applied bias potential below 0.8 V enhanced the photocatalytic degradation of RhB by promoting the separation and transfer of photogenerated holes and electrons. At the potential between 0.8 and 1.0 V, the degradation of RhB was further enhanced, which is induced by direct electro-oxidation and photocatalysis. At the potential greater than 1.3 V, indirect electro-oxidation of RhB occurred with the largest synergetic effect. The synergetic effect can also increase the mineralization degree of the RhB. On the basis of the X-ray photoelectron spectra (XPS) analysis of the surface of the electrode after electrochemical reaction, the electropolymerization occurred which blocked the electrode and slowed the electro-oxidation of RhB. Active species generated via the photocatalytic process can activate the passivated electrode and promote the electro-oxidation of RhB. The O2 electrochemically generated at the anode promoted the photocatalysis by capturing the photogenerated electrons and may induce the formation of H2O2. Thus, more active species could be formed through new reactive routines in the photoelectrocatalytic (PEC) process. RhB degradation was mainlythrough decomposition of the conjugated chromophore structure with slight occurrence of de-ethylation. The stability of the electrode in the PEC process was confirmed based on the XPS and Raman analysis.     

Anchored oxygen-donor coordination to iron for photodegradation of organic pollutants

A photocatalyst of oxygen-donor coordination to iron, complex of 5-sulfosalicylic acid (SSA) with ferric ion, supported on resin to cycle Fe3+/Fe2+ center under visible irradiation can effectively generate *OH radicals from H2O2, leading to degradation of organic pollutants in water. The higher turnover number was achieved by this catalyst for the degradation of model compound than those reported for the general N-donor ligands catalysts. The reversible "on/ off" switching of Fe3+/Fe2+ complexation with SSA, coupled with the phenol/phenoxyl radical conversion of the o-phenoxyl moiety of SSA, produces an ideal catalytic system that separates the Fenton reaction and the followed oxidations by *OH radicals (in water phase) from the regeneration of the catalytic species, Fe (SSA)2-, which occurs on the surface of resin. This system not only inhibits the undesired destruction of the ligands by *OH radicals, improving the stability of the catalyst, but also avoids the unnecessary decomposition of H2O2 into HO2* that occurs in the homogeneous Fenton system. Therefore, the system suggests an efficient utilization of H2O2 for degradation of organic pollutants.     

直接染料和阳离子染料对棉和苎麻的染色差异性

用直接染料和阳离子染料分别对棉和苎麻织物进行染色,测定了染色织物的L*a*b*值,并计算了同一染料在相同条件下对两种织物的彩度差值、色差值和K/S差值。结果表明,几种染料对棉和苎麻的染色存在不同程度的差异性,用直接染料和阳离子染料染色的棉织物的K/S值和彩度值明显高于苎麻织物;使用直接耐酸大红4BS、直接枣红GB、直接冻黄G、直接黄棕D3G、阳离子嫩黄O、阳离子艳蓝RL对棉和苎麻的织物进行染色时,棉和苎麻织物之间的色差值均大于5。     

Enhanced sonocatalytic degradation of azo dyes by Au/TiO2

Au-loaded TiO2 (Au/TiO2) has been reported for the first time as a sonocatalyst. It was found that the catalyst Au/TiO2, with a low Au loading 0.5 wt % and under common and commercial frequency (40 kHz) ultrasonic irradiation, greatly accelerated both the discoloration and total organic carbon (TOC) removal of azo dyes such as orange II (Org II), ethyl orange (EO), and acid red G (ARG), as compared to bare TiO2 and nano-Au catalyst. About 80% TOC removal was achieved after complete discoloration of 2.5 x 10(-4) M Org II. H2O2 and H2 formation as well as their accumulation was greatly enhanced due to Au loading on TiO2. Both oxidative and reductive degradation intermediates have been detected, and thus the mechanism involves both enhanced oxidation and enhanced reduction via the accelerated formation of active *OH and *H radicals due to Au loading on TiO2, which is supported by electron spin resonance (EPR) and other evidence. The study provides an admirable way to raise the efficiency of sonication and to treat azo dye-containing wastewaters with sonocatalytic processes.     

活性炭负载磷钨酸催化合成香料苹果酯-B

制备了环境友好催化剂活性炭负载磷钨酸H3PW12O40/C，并以H3PW12O40/C为催化剂催化合成了香料苹果酯-B。得到了苹果酯-B合成的适宜工艺条件：n（1，2-丙二醇）：n（乙酰乙酸乙酯）=1．5：1，H3PW12O40/C负载量为23．1％，H3PW12O40/C用量为反应物总质量的1．0％，反应时间为120min，苹果酯-B的收率为84．8％，目的产物经红外光谱、质谱和元素分析确证。     

Iodine-Sensitized Degradation of 2,4,6-Trichlorophenol under Visible Light

Molecular iodine has been studied, for the first time, as a sensitizer for the degradation of 2,4,6-trichlorophenol (TCP) in aqueous solution under visible light (λ ≥ 450 nm). TCP was degraded in the presence of commercial I(2), but the reaction rate decreased significantly after 2 h. When a solution of NaI and H(2)O(2) was used as an iodine source with phosphotungstic acid (PW) as a catalyst, TCP degradation was not only fast but also followed zero-order kinetics. Importantly, the I(2) concentration remained unchanged with time, indicative of I(2) recycling as a kind of photocatalyst. During TCP degradation, 2,6-dichloro-1,4-benzoquinone was produced as the main intermediate (76%), which slowly degraded in the irradiated solution. For every equivalent of TCP consumed at the 2 h time point, approximately 1.7 equivalents of chloride ions were produced. Further study of the effect of variables including the type of polyoxometalates (POM) and the initial concentration of each component revealed that the rate of TCP degradation under visible light was determined by the rate of I(2) production in the dark. The optimum pH and apparent activation energy for TCP disappearance were 4.5 and 42.8 kJ/mol, respectively. It is proposed that TCP degradation is initiated by iodine radicals produced from I(2) photolysis, followed by I(2) regeneration through a POM-catalyzed oxidation of I(3)(-) by H(2)O(2).     

Photocatalytic degradation of RhB by fluorinated Bi2WO6 and distributions of the intermediate products

Fluorinated Bi2WOs catalyst was synthesized by a simple hydrothermal process. The effects of fluorine doping on crystal structure, optical property, photoinduced hydrophilicity, surface acidity, and photocatalytic activity of the as-prepared sample were observed in detail. Fluorinated Bi2WOs presented the enhanced photoactivity for the RhB degradation under the simulative sunlight (lamda > 290 nm), which could be a synergetic effect of the surface fluorination and the doping of crystal lattice. To get a better handle on the mechanistic details of this photocatalytic system, the photodegradation process of RhB was examined. In the fluorinated Bi2WO6 system, five intermediates, namely, N,N-diethyl-N'-ethylrhodamine, N,N-diethylrohodamine, N-ethyl-N'-ethylrhodamine, N-ethylrhodamine, and rhodamine were thus identified, whereas the first three intermediates could only be identified in the case of the Bi2WO6 system. This result indicated that more RhB molecules were degraded via the deethylation process in the fluorinated Bi2WO6 system. It was proposed that the (F-)-containing function on the catalyst surface could serve as an electron-trapping site and enhance interfacial electron-transfer rates by tightly holding trapped electrons. On the basis of the experimental results, a photocatalytic mechanism was discussed in detail.     

Degradation of organic dyes via bismuth silver oxide initiated direct oxidation coupled with sodium bismuthate based visible light photocatalysis

Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting a > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes.     

铁改性腈纶纤维催化剂在偶氮染料降解反应中的应用

使用水合肼和盐酸羟胺对腈纶纤维进行表面改性,然后将其与铁离子反应制得铁改性腈纶纤维催化剂（PAN-Fe）。在过氧化氢存在条件下将PAN-Fe催化剂应用于2种水溶性阴离子偶氮染料的光催化氧化降解反应中,考察了催化剂添加量、催化剂表面铁离子含量、染料浓度和pH值对染料降解反应的影响。结果表明,尽管PAN-Fe催化剂在暗态能催化染料降解反应,但是光辐射可促进其催化作用的提高;催化剂添加量及其表面铁离子含量的增加能够明显提高染料的脱色率。在PAN-Fe催化剂存在下染料降解反应可在碱性条件下进行,但是染料浓度的增加会使其脱色率降低。     

Pd-catalytic in situ generation of H2O2 from H2 and O2 produced by water electrolysis for the efficient electro-fenton degradation of rhodamine B

A novel electro-Fenton process was developed for wastewater treatment using a modified divided electrolytic system in which H2O2 was generated in situ from electro-generated H2 and O2 in the presence of Pd/C catalyst. Appropriate pH conditions were obtained by the excessive H+ produced at the anode. The performance of the novel process was assessed by Rhodamine B (RhB) degradation in an aqueous solution. Experimental results showed that the accumulation of H2O2 occurred when the pH decreased and time elapsed. The maximum concentration of H2O2 reached 53.1 mg/L within 120 min at pH 2 and a current of 100 mA. Upon the formation of the Fenton reagent by the addition of Fe2+, RhB degraded completely within 30 min at pH 2 with a pseudo first order rate constant of 0.109 ± 0.009 min(-1). An insignificant decline in H2O2 generation and RhB degradation was found after six repetitions. RhB degradation was achieved by the chemisorption of H2O2 on the Pd/C surface, which subsequently decomposed into ?OH upon catalysis by Pd0 and Fe2+. The catalytic decomposition of H2O2 to ?OH by Fe2+ was more powerful than that by Pd0, which was responsible for the high efficiency of this novel electro-Fenton process.