Carbon dioxide reduction under visible light: a comparison of cadmium sulfide and titania photocatalysts

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Phase-compositional control and visible light photocatalytic activity of nitrogen-doped titania via solvothermal process

Nitrogen-doped titania nanoparticles consisted of pure anatase, rutile and brookite phases were successfully prepared by a solvothermal process in TiCl₃-HMT (hexamethylenetetramine, C₆H₁₂N₄)-alcohol mixed solution. The powders were yellow or beige and showed excellent visible light absorption and photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light of wavelength >510 nm.     

Surfactant mediated synthesis of spherical binary oxides photocatalytic with enhanced activity in visible light

Spherical silica and zirconia mixed titania and pure titania samples were prepared in presence of cetyltrimethylammonium bromide (CTAB) through controlled hydrolysis of corresponding metal alcoxides. Effect of surfactant amount and calcinations temperature on morphology, surface area and photocatalytic activity is studied using PXRD, SEM, FTIR, Solid state UV-vis spectroscopy and BET surface area. It is well observed that in presence of 2 mol% CTAB, uniform sized spherical oxide particles can be synthesized. However, increasing or decreasing the surfactant amount does not favor the spherical particle formation. Material synthesis in presence of CTAB not only helps in the spherical particle formation but also increases the surface area and visible light absorption. Studies on photocatalytic lead removal with respect to calcination temperature indicate that the calcination at 500 degrees C is most suitable for the best photocatalytic activity. Mixing of zirconia and silica helps in anatase phase stabilization even at 900 degrees C calcination. Accordingly low decrease in surface area even at 900 degrees C calcination is observed. Due to the phase stabilization and higher surface area binary oxide materials showed comparatively better photocatalytic activity even after calcination at 900 degrees C. So it can be concluded that present synthesis approach can produce uniform sized spherical binary oxide materials with better photocatalytic activity in visible light.     

紫外和可见光照射下Fe-TiO2复合材料催化低浓度芳香族有机污染物降解（英文）

Fe‐TiO2 photocatalysts with different ratios of Fe to Ti were prepared by a sol‐gel process using tetra‐n‐butyl titanium and iron(III) nitrate as Ti and Fe sources, respectively. The photocatalytic function of the prepared composites was examined for the decomposition of low‐concentration(0.1 ppm) airborne benzene, toluene, ethyl benzene, and o‐xylene(BTEX). The Fe‐TiO2 composites were characterized by energy dispersive X‐ray spectroscopy, X‐ray diffraction, UV‐visible spectroscopy, and Fourier transform infrared spectroscopy. The time‐series ratios of outlet to inlet concentrations of toluene, ethyl benzene, and o‐xylene target chemicals, as determined by the Fe‐TiO2 composites under visible light exposure, were lower than or similar to those of the reference TiO2 photocatalyst. Moreover, the time‐series ratios of outlet to inlet concentrations of the three compounds, as determined for the Fe‐TiO2 composites, increased as the ratio of Fe to Ti increased from 0.001 to 0.010. In contrast, under UV exposure, the time‐series ratios of outlet to inlet concentrations of BTEX, determined for the Fe‐TiO2 composites, were similar to or higher than those obtained from the reference TiO2 photocatalyst. Fe‐TiO2 composites with an optimal Fe to Ti ratio could effectively be applied for the purification of low‐concentration aromatic organic pollutants.     

Thermo-photocatalytic oxidation of benzene under visible light over nitrogen-doped titania grafted with Cu and Pt

Nitrogen-doped titania (TiO₂-N) was synthesized and tested, both in unmodified form and with grafted Cu and Pt particles, in the reaction of photocatalytic oxidation of benzene under visible light irradiation at temperatures of 40, 100 and 140 °C. The results obtained indicate additional thermal activation of the reaction over Pt-containing samples with the maximum difference between the total and thermal activities at 100–120 °C. As modifiers, both platinum and copper separately improve the photoactivity of TiO₂-N, but when used together, their effects do not add up, and the photocatalyst behaves like a Pt-modified sample.     

Effect of Mie resonance on photocatalytic hydrogen evolution over dye-sensitized hollow C-TiO_2 nanoshells under visible light irradiation

Light utilization is one of the key factors for the improvement of photocatalytic perfo rmance.He rein,we design C-TiO_2 hollow nanoshells with strong Mie resonance for enhanced photocatalytic hydrogen evolution in a dye-sensitized system under visible light irradiation(λ≥420 nm).By tuning the inner diameters of hollow nanoshells,the Mie resonance in hollow nanoshells is adjusted for better excitation of dye molecules,which thus greatly enhances the light utilization in visible light region.This work shows the potential of Mie resonance in nanoshells can be an alternative strategy to increase the light utilization for photocatalysis.     

Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light

Hydrated titania was prepared by a sol-gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method. The materials were characterized by various advanced techniques such as PXRD, BET surface area, N(2) adsorption-desorption measurements, FTIR, and SEM. Analytical results demonstrated that TiO(2) is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO(2). It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts. The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials. Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated. At 2.5 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO(2). The photocatalytic degradation followed first-order kinetics.     

Preparation and photocatalytic activity under visible light irradiation of mesostructured titania particles modified with phthalocyanine in the pores

Mesostructured titania particles modified with phthalocyanine (Pc) were prepared by using molecular self-assemblies of cetyltrimethylammonium bromide (CTAB) with solubilized Pc as a template. Low-angle X-ray diffraction pattern and transmission electron microscopy (TEM) image clearly show the formation of Pc/titania particles with hexagonal mesopore structures. Diffuse reflectance UV–vis spectrum and fluorescence spectrum of Pc/titania indicate that Pc molecules in the pores are in a monomeric state. In addition, Pc/titania particles have photocatalytic activity under visible light irradiation (>610 nm) due to the reduction reaction by the electrons transferred from Pc to titania.     

The photocatalytic activity of TiO2 foam and surface modified binary oxide titania nanoparticles

Surface modified titania dioxide composite nanoparticles prepared by hydrogen reduction reaction and a mesoporous TiO₂ foam made from a surface modifier and a long chain organic surfactant were characterized by diffractive, spectroscopic and microscopic techniques and studied for their catalytic activity towards the decomposition of an industrial water pollutant, methyl orange. The surface deposition of ruthenium and silicon particles improved the photocatalytic activity of the composite particles resulting in a faster decomposition of the methyl orange compared to commercial TiO₂ alone. Modification of TiO₂ with RuO₂ only offered a marginal benefit over TiO₂ while the incorporation of RuO₂ and SiO₂ into TiO₂ resulted in a marked increase in the rate constant and catalytic activity. These results are consistent with the enhanced surface properties of the composite materials resulting from the modification of TiO₂ with RuO₂ and SiO_2. This surface enhancement effects appear synergetic to the charge separation process and hence the photocatalytic results are explained on the basis of a mechanism involving efficient charge transfer across the interfaces of the composites involving photogenerated electron–hole pairs. Results obtained in this study show that the percentage degradation after 1 h of illumination was 47.15% for TiO₂ foam, 75.5 and 106.4%, respectively, for TiO₂/RuO₂ (SiO₂ 5%, w/w) and TiO₂/RuO₂(SiO₂ 10%, w/w) and 34.15% for commercial TiO₂.     

Improved visible light photocatalytic activity of titania loaded with silver on discoloration of a heterocyclic aromatic chemical dye solution

The photocatalytic activity of silver deposited Degussa P25 titanium dioxide (Ag-DP25) in the photodegradation of methylene blue (MB) was investigated. The as-prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), infrared spectra and surface photovoltage spectroscopy (SPS) techniques. The obtained results show that the silver dopant could effectively inhibit the recombination of the photoinduced electron and holes, improving the absorption capability for visible light of photocatalyst and leading to increased surface OH group density. The degradation experiment reveals that the catalytic property of Ag-DP25 in the degradation of MB dye is more efficient than that of commercially available Degussa P25 TiO₂ (DP25) samples under visible-light irradiation. Besides, degradation kinetics of MB dye can, be well described by Langmuir-Hinshelwood equation and shows pseudo-first order law.     

Effect of chromium doping on the electrical and catalytic properties of powder titania under UV and visible illumination

Although Cr-doped (0.85 at%) TiO₂ absorbs in the visible region, it becomes a photoconductor only through band-gap illumination and the doping causes a considerable decrease in photoconductance. Its activity for oxidations (oxalic acid, propene, 2-propanol) and for oxygen isotope exchange is nil under visible illumination and is 25–1000 times diminished under UV light. This is attributed to an increase in electron—hole recombination at the Cr³⁺ ion sites. Conversely, similar doping might be envisaged to enhance the light stability of TiO₂-containing materials if the colorimetric properties were maintained.     

Wavelength-sensitive photocatalytic degradation of methyl orange in aqueous suspension over iron(III)-doped TiO2 nanopowders under UV and visible light irradiation

Well-crystallized iron(III)-doped TiO2 nanopowders with controlled Fe3+ doping concentration and uniform dopant distribution, have been synthesized with plasma oxidative pyrolysis. The photocatalytic reactivity of the synthesized TiO2 nanopowders with a mean particle size of 50-70 nm was quantified in terms of the degradation rates of methyl orange (MO) in aqueous TiO2 suspension under UV (mainly 365 and 316 nm) and visible light irradiation (mainly 405 and 436 nm). The photodecomposition of MO over TiO2 nanopowders followed a distinct two-stage pseudo first order kinetics. Interestingly, the photocatalytic reactivity depends not only on the iron doping concentration but also on the wavelength of the irradiating light. Under UV irradiation, nominally undoped TiO2 had much higher reactivity than Fe3+ -doped TiO2, suggesting that Fe3+ doping (> 0.05 at. %) in TiO2 with a mean particle size of approximately 60 nm was detrimental to the photocatalytic decomposition of methyl orange. Whereas, under visible light irradiation, the Fe3+ -doped TiO2 with an intermediate iron doping concentration of approximately 1 at. % had the highest photocatalytic reactivity due to the narrowing of band gap so that it could effectively absorb the light with longer wavelength. A strategy for improving the photocatalytic reactivity of Fe3+ -doped TiO2 used in the visible light region is also proposed.     

Selective visible light reduction of carbon dioxide over iridium(III)-terpyridine photocatalysts

The CO₂ reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy conversion and chemical manufacturing processes. Here, we report two new iridium (III) terpyridine-based photocatalysts capable of selective reduction of CO₂ to CO under visible light (λ ≥ 420 nm). The first photocatalyst, [Ir–COOH], was functionalized with the carboxyl group on the phenylpyridine, whereas the second, [Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The [Ir-PhCOOH] was characterized by a higher extinction coefficient than [Ir–COOH], thus allowing more absorption of photons. Although both photocatalysts require two-electron activation, the [Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir center. These photocatalysts show exclusive selectivities in the production of CO. The turnover frequencies for [Ir–COOH] and [Ir-PhCOOH] were 19 and 10 h^?1, respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate-limiting step in the conversion of 1COOH to 1CO, and where the barrier is significantly lower for [Ir-PhCOOH] than for [Ir–COOH].     

BiOBr/BiOI复合体的制备及可见光催化性能

以硝酸铋、碘化钾、溴化钠和聚乙二醇-400为主要原料,利用水热法制备出具有较小粒径的BiOBr/BiOI复合体,通过扫描电子显微镜(SEM)、X射线衍射(XRD)、紫外可见漫反射(DRS)等测试手段对样品的形貌、物相组成进行了表征。以罗丹明B为模拟污染物,研究了可见光下所制备样品的光催化性能。结果表明:BiOBr/BiOI复合体的光催化性能高于单一的BiOBr和BiOI,光照80 min后罗丹明B的降解效率可达95.6%。     

Preparation of mesoporous TiO2/CNT nanocomposites by synthesis of mesoporous titania via EISA and their photocatalytic degradation under visible light irradiation

Stabilized mesoporous TiO₂ was synthesized by evaporation induced self assembly (EISA) method and mechanically incorporated into single-walled carbon nanotubes (SWCNT) with different ratios. The physicochemical properties of the nanocomposites (mesoporous TiO₂/SWCNT) materials were investigated by Brunauer–Emmett–Teller (BET) measurement, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), photoluminescence (PL) and ultraviolet–visible (UV–Vis) spectroscopy measurements. The catalytic activity of mesoporous TiO₂ and nanocomposites were assessed by examining the degradation of rhodamine B as model aqueous solution under visible light. CNTs are facilitating the photocatalytic activity of mesoporous TiO₂ in the degradation of rhodamine B efficiently.     

Physicochemcial characteristic of CdS-anchored porous WS2 hybrid in the photocatalytic degradation of crystal violet under UV and visible light irradiation

In this work, we report the synthesis of CdS-incorporated porous WS₂ by a simple hydrothermal method. The structural, morphological, and optical properties of the samples were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), high resolution X-ray photoelectron spectroscopy (XPS) and UV–visible spectrometry. The photocatalytic activities were established for degradation of crystal violet (CV) under UV and visible light irradiation. The CdS-incorporated porous WS₂ hybrid demonstrated high photocatalytic activity for degradation of CV pollutant compared to pure CdS nanoparticles and porous WS₂ sheets. This result implies that the CdS-incorporated porous WS₂ promoted more electron-hole pair transformation under UV and visible light irradiation. This significant enhancement of photocatalytic efficiency of CdS-incorporated porous WS₂ photocatalyst under visible light can be ascribed to the presence of CdS nanospheres on the meshed-like WS₂ sheets which potentially improves absorption in the visible range enabled by surface plasmon resonance effect of CdS nanospheres. The photostability and reusability of the CdS-porous WS₂ were examined through recycling experiments.     

Photocatalytic activity of silicon nanowires under UV and visible light irradiation

The communication reports on the high performance of hydrogen-terminated silicon nanowires and silicon nanowires coated with metal (Ag, Cu) nanostructures for the photodegradation of rhodamine B under UV and visible light irradiation.     

Controllable synthesis of titania/reduced graphite oxide nanocomposites with various titania phase compositions and their photocatalytic performance

A facile method is presented for preparing TiO2 /reduced graphite oxide(RGO) nanocomposites with phase-controlled TiO2 nanoparticles via redox reaction between the reductive titanium(Ⅲ) precursor and graphite oxide(GO),and a series of TiO2 /RGO composites with various TiO2 phase compositions were obtained.In all the titania/RGO composites,the TiO2 nanoparticles were uniformly distributed on the surface of the RGO.The TiO2 consisted of anatase phase particles in the form of square-plates with edges less than 10 nm and the rutile phase nanorods in diameters less than 10 nm.The performances of the as-prepared TiO2 /RGO composites were investigated on catalytically degrading phenol under visible light irradiation.The TiO2 /RGO composites can effectively degrade phenol under visible light irradiation,and the phase composition of TiO2 in the composites significantly influences the activities of these catalysts.