Photocatalytic degradation of phenol under solar radiation using microwave irradiated zinc oxide

The effect of preparation method on the photocatalytic degradation of phenol using zinc oxides under solar radiation was studied in batch reactors. Zinc oxide was prepared by different methods by varying precipitating agents and the source of precursors and microwave irradiation time and characterized by XRD, surface area, acid sites and crystallite sizes. The photocatalytic reactions were carried out by varying the reaction conditions such as preparation methods, microwave irradiation time, activation temperature, solar irradiation time, catalyst amount, substrate concentration etc. Under optimization conditions, it was found that 15 min microwave irradiated sample shows 88% phenol (0.6 g/l dose) degradation at pH 5.0 and 4 h reaction time under sunlight. Zinc oxide samples prepared by microwave irradiation and calcined at 573 K exhibit highest surface area, acid sites and lowest crystallite sizes and show highest activity towards photocatalytic oxidation of phenol.     

Decoration of Pt on the metal free RGO-TiO2 composite photocatalyst for the enhanced photocatalytic hydrogen evolution and photocatalytic degradation of pharmaceutical pollutant β blocker

Easy synthesis of graphene based composite photocatalyst with the incorporation of minimal quantity of noble metals for the enhanced photocatalytic hydrogen evolution as well as photocatalytic degradation and mineralization of recalcitrant pollutants under solar irradiation is an urgent requirement from the clean energy and environment point of view all over the globe. Herein, we demonstrate the decoration of Pt by photodeposition method on the hydrothermally synthesized RGO-TiO₂ nanocomposite. The various photocatalysts synthesized were successfully characterized by XRD, FTIR, Raman, UV–visible absorption spectra, XPS, SEM and TEM techniques. The well characterized photocatalysts were further investigated for the photocatalytic hydrogen evolution studies of methanol water mixtures under UV as well as simulated solar light irradiation. The optimized Pt-RGO-TiO₂ (1 wt % Pt and 10 wt % RGO) composite was found to show 14 fold increase in the photocatalytic hydrogen evolution efficiency under UV light irradiation and 20 fold increase under simulated solar light irradiation as compared to bare TiO₂ under UV light irradiation. The ternary photocatalyst showed very good recycle and reuse capability up to 4 cycles. The optimized Pt-RGO-TiO₂ was further tested for the enhanced photocatalytic degradation and mineralization of pharmaceutical pollutant namely β blocker Propranolol under UV as well as simulated solar light irradiation. The obtained results showed 79% and 94% reduction in COD of Propranolol under UV and simulated solar light irradiation respectively. The appreciable enhancement in the photocatalytic activity of the Pt decorated RGO-TiO₂ photocatalyst as compared to bare TiO₂ under UV and simulated solar light can be attributed to the use of maximum range of solar spectrum along with their excellent properties of charge separation by RGO and Pt.     

Photocatalytic degradation of organic compounds in aqueous solution by a TiO2-coated rotating-drum reactor using solar light

This paper deals with the degradation of aqueous phenol by a newly proposed rotating-drum reactor coated with a TiO₂ photocatalyst, in which TiO₂ powders loaded with Pt are immobilized on the outer surface of a glass-drum. The reactor can receive solar light and oxygen from the atmosphere effectively. It was shown experimentally that phenol can be decomposed rapidly by this reactor under solar light: with our experimental conditions the phenol with an initial concentration of 22.0 mg/dm³ was decomposed within 60 min and was completely mineralized through intermediate products within 100 min. The photonic efficiency under solar light was shown to take the value 0.00742 mol-C/Einstein. The photocatalytic decomposition processes of phenol by this reactor were also discussed on the basis of the Langmuir–Hinshelwood kinetic model.     

可见光响应型改性纳米二氧化钛催化降解生物质气化洗焦废水

制备了可见光响应型改性纳米二氧化钛催化剂,用于处理生物质气化洗焦废水,考察了催化剂改性方式对苯酚和洗焦废水COD去除的影响。实验结果表明：以Ag-C/TiO2为催化剂,在可见光下照射10 h,苯酚的COD去除率可达43.5%,洗焦废水的COD去除率达26.8%;在太阳光下照射36 h,洗焦废水的COD去除率达到90.9%。改性纳米Ag-C/TiO2催化剂在可见光下具有良好的催化活性,对洗焦废水有较好的处理效果。     

Photocatalytic degradation of organic dyes with Er:YAlO3/ZnO composite under solar light

The Er³⁺:YAlO₃/ZnO composite, a new photocatalyst that could effectively utilize visible light, was prepared by ultrasonic dispersion and liquids boiling method in this work. In succession, the Er³⁺:YAlO₃/ZnO composite, Er³⁺:YAlO₃ particle and pure ZnO powder were characterized by X-ray diffraction (XRD). The Acid Red B dye as a model compound was degraded under solar light irradiation to evaluate the photocatalytic activity of the Er³⁺:YAlO₃/ZnO composite. In addition, the effects of Er³⁺:YAlO₃ content, heat-treated temperature and heat-treated time on photocatalytic activity of Er³⁺:YAlO₃/ZnO composite were reviewed through the degradation of Acid Red B dye under solar light. Otherwise, the effects of initial concentration, Er³⁺:YAlO₃/ZnO amount, solution acidity and solar light irradiation time on the photocatalytic degradation of Acid Red B dye were investigated in detail. It was found that the photocatalytic activity of Er³⁺:YAlO₃/ZnO composite is much higher than that of pure ZnO powder for the similar system. Perhaps, the use of this Er³⁺:YAlO₃/ZnO composite may provide a new way to take advantage of ZnO in sewage treatment aspects using solar energy.     

Large solar plant photocatalytic water decontamination: Effect of operational parameters

The effect of the concentration of the photocatalyst, the organic substrate and the light intensity is presented for the photocatalytic degradation of pentachlorophenol in the large solar plant built at the Plataforma Solar de Almeria. The degradation of pentachlorophenol is easily achieved in short residence times. The main factors affecting the total efficiency are discussed in view of a simple model for the primary events in the photocatalytic system. The derived approximated equations are able to fit the experimental data well. The optimization of the degradation and mineralization rates is strongly dependent on the organic substrate and predominantly depends on kinetic factors. The partition or competition of the substrate and its degradation products on the surface of the photocatalyst seems unimportant.     

Visible-light-assisted photocatalytic degradation of gaseous formaldehyde by parallel-plate reactor coated with Cr ion-implanted TiO2 thin film

Sol–gel nano titanium dioxide (TiO₂) thin film can be activated by the ultraviolet (UV) radiation available in sunlight to perform solar photocatalysis. The useful spectral range can be extended from UV to visible light by implantation of metal ion into the TiO₂ lattice. As a result, the solar visible light can be utilized more efficiently to enhance the solar photocatalysis. In this study, visible-light-assisted photocatalytic glass reactors were built by parallel borosilicate glass plates coated on the upper surfaces with sol–gel TiO₂ thin films implanted with chromium (Cr) ion. The properties of the Cr/TiO₂ thin films were fully characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal gravity (TG) analysis, scanning-electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. In the performance tests, a metal halide lamp was used as an external light source to resemble the solar visible spectral radiation. The performance of a Cr/TiO₂ photoreactor was measured in terms of its photocatalytic degradation of gaseous formaldehyde in a single pass of contaminated air flowing through the photoreactor. The experimental results demonstrated the promise of using light-transmitting glass substrate to allow transmission and distribution of light from an external source to achieve solar photocatalysis. In the design of a parallel-plate photoreactor, it is important to properly control the Cr ion loading so that each Cr/TiO₂-coated glass plate absorbs a portion of the incident light for its photocatalytic activation and allows light transmission available for the remaining coated plates.     

The preparation of TiO2–nitrogen doped by calcination of TiO2·xH2O under ammonia atmosphere for visible light photocatalysis

The investigation on incorporating nitrogen group into titanium dioxide in order to obtain powdered visible light-active photocatalysts is presented. The industrial hydrated amorphous titanium dioxide (TiO₂·xH₂O) obtained directly from sulphate technology installation was modified by heat treatment at temperatures of 100–800 °C for 4 h in an ammonia atmosphere. The photocatalysts were characterized by UV–VIS–DR and XRD techniques. The UV–VIS–DR spectra of the modified catalysts exhibited an additional maximum in the VIS region (, ) which may be due to the presence of nitrogen in TiO₂ structure. On the basis of XRD analysis it can be supposed that the presence of nitrogen does not have any influence on the transformation temperature of anatase to rutile. The photocatalytic activity of the modified photocatalysts was determined on the basis of decomposition rate of phenol and azo-dye (Reactive Red 198) under visible light irradiation. The highest rate of phenol degradation was obtained for catalysts calcinated at 700 °C (6.55%), and the highest rate of dye decomposition was found for catalysts calcinated at 500 and 600 °C (ca. 40–45%). The nitrogen doping during calcination under ammonia atmosphere is a very promising way of preparation of photocatalysts which could have a practical application in water treatment system under broader solar light spectrum.     

TiO2-fixed-bed reactor for water decontamination using solar light

A photocatalytic reactor using immobilized TiO₂ (Degussa P25) on a glass plate was studied on a bench scale using solar light as the source of radiation. The influence of parameters such as the slope of the plate, solar light intensity, flow rate and molar flow rate, as well as the geometry of the reactor, was studied using dichloroacetic acid (DCA) as a model compound. A linear dependence of degradation with solar light intensity, measured at 365 nm, was observed. Experiments with recirculation as well as a single pass of solution suggested no mass transfer limitations in this system. The mineralization of DCA resulted in the production of quantitative amounts of chloride ions. An initial concentration of 5 mmol/L of DCA decayed to 2 mmol/L in about 2 min of irradiation. An exponential decay of degradation was observed with an increase of the molar flow rate, achieving saturation around 1.5 mmol DCA/min.     

An experimental and theoretical study of the effect of Ce doping in ZnO/CNT composite thin film with enhanced visible light photo-catalysis

Ce-doped ZnO/CNT composite thin film was fabricated successfully on soda-lime-silica glass substrate by sol-gel drop coating method. The structure and morphology of nanocrystalline Ce-doped ZnO/CNT thin film were characterized by X-ray Diffraction (XRD), X-ray photo-electron spectroscopy (XPS), Field Emission Scanning Electron Microscope (FESEM) and UV–Visible spectroscopy. The photocatalytic activity of Ce-doped ZnO/CNT thin film was evaluated by photocatalytic degradation of methylene blue (MB) in aqueous solution as a model pollutant under visible light irradiation. The synthesized Ce-doped ZnO/CNT composite thin film showed 76.71% photocatalytic efficiency whereas bare ZnO thin film showed that of only 25.30%. It has been reported that improved photocatalytic efficiency of composite is due to the synergistic effect of Ce doping and insertion of CNTs into ZnO matrix. The experimental photodegradation data were well fitted to first-order kinetics. The photocatalytic activity of the prepared thin film can be regenerated, which implies that the photocatalytic degradation process could be operated at a relatively low cost. The results suggest that Ce-doped ZnO/CNT composite thin film prepared by sol-gel drop coating method can be developed as an economically feasible and environmentally friendly method to degrade dye containing wastewater using visible light. Furthermore, atomic models for Ce doping in ZnO cluster was used to investigate the effect of doping on electronic structure of ZnO through density functional theory calculations. The computational study suggested a significant narrowing of the band gap and change of the maximum absorption bands towards higher wavelength. These all support the experimental results.     

The fabrication of magnetic recyclable nitrogen modified titanium dioxide/strontium ferrite/diatomite heterojunction nanocomposite for enhanced visible-light-driven photodegradation of tetracycline

Powdery photocatalyst has long been studied in various aspects, yet its low recovery in suspension system is still the bottleneck which hinders its practical application. An alternative method to overcome this shortcoming is to develop magnetic recyclable ferrite-based hybrid photocatalyst. In this work, we prepared nitrogen modified titania/strontium ferrite/diatomite (N-TSD) ternary hybrid via sol-gel method. The physicochemical properties of various hybrid catalysts were characterized and studied, and their photocatalytic properties were evaluated via the degradation of antibiotic tetracycline (TC) under visible light. The formation of heterojunction between N modified TiO₂ and strontium ferrite hindered the recombination of photo-induced charge carriers and improved the photocatalytic activity. The photodegradation rate of TC was accelerated by the high adsorption ability of diatomite, due to the adsorption and degradation synergistic effect between catalysts and substrate diatomite. Based on the degradation results, the optimal N dopant amount, as well as optimal catalyst dosage was determined. The ternary N-TSD composite could simply be recovered from TC solution via an external magnet, and the repetition tests indicated no obvious decrease of photoactivity, even after 5 turns. This nanocomposite was considered appropriate to be applied in wastewater remediation process, thanks to its high photocatalytic efficiency under visible light irradiation, as well as its good reusability and stability.     

Solar photocatalytic mineralization of isoproturon over TiO2/HY composite systems

The present investigation covers immobilization of titanium dioxide over HY support for the treatment of isoproturon pesticide. Catalysts are characterized by XRD, SEM–EDAX, TEM, BET surface area and UV–vis DRS. A detailed photocatalytic degradation study under solar light in aqueous suspensions with parameters like loading of TiO₂ over HY, amount of the catalyst, concentration of substrate, pH effect, durability of the catalyst and comparison between suspended TiO₂ and supported systems are reported. Mineralization of isoproturon is monitored by total organic carbon, chemical oxygen demand and a plausible mechanism is proposed for photocatalytic degradation based on degradation products.     

Solar photocatalytic degradation of azo dye: comparison of photocatalytic efficiency of ZnO and TiO2

The photocatalytic activity of commercial ZnO powder has been investigated and compared with that of Degussa P25 TiO₂. Laboratory experiments with acid brown 14 as the model pollutant have been carried out to evaluate the performance of both ZnO and TiO₂ catalysts. Solar light was used as the energy source for the photocatalytic experiments. These catalysts were examined for surface area, particle size and crystallinity. The effect of initial dye concentration, catalyst loading, irradiation time, pH, adsorption of acid brown 14 on ZnO and TiO₂, intensity of light and comparison of photocatalytic activity with different commercial catalysts were studied. The progress of photocatalytic degradation of the acid brown 14 has been observed by monitoring the change in substrate concentration of the model compound employing HPLC and measuring the absorbance in UV–Visible spectrophotometer for decolourisation. The photodegradation rate was determined for each experiment and the highest values were observed for ZnO suggesting that it absorbs large fraction of the solar spectrum and absorption of more light quanta than TiO₂. The complete mineralisation was confirmed by total organic carbon (TOC) analysis, COD measurement and estimation of the formation of inorganic ions such as NH₄⁺, NO₃⁻, Cl⁻ and SO₄²⁻.     

Destruction of phenol in water with sun, sand, and photocatalysis

The photocatalytic degradation and oxidation to carbon dioxide of aqueous phenol solutions have been studied using natural sunlight in geometries simulating shallow ponds. The photocatalyst was titanium dioxide freely suspended in the solution or immobilized on sand or silica gel. Photodegradation rates were approximately three times faster with the free suspension than with the immobilized catalyst under the same conditions, and were dependent on the time of the year and the time of the day. The seasonal variation correlated roughly with seasonal solar irradiance tabulations for the UV component of the spectrum. For 10 ppm of phenol the maximum rate of solar degradation resulted in a decrease in concentration to 10 ppb in less than 80 min with total mineralization in 110 min. Maintaining the same geometry, 30 L of solution covering 1 m² would degrade to the same extent.     

Co-application of liquid phase plasma process for hydrogen production and degradation of acetaldehyde over NiTiO2 supported on porous materials

Photocatalytic decomposition of acetaldehyde-contained wastewater was assessed for the degradation of pollutants and the production of hydrogen. Liquid phase plasma was applied in the photoreaction as a light source. The evolution of hydrogen and acetaldehyde degradation were characterized by the photocatalytic decomposition system. Ni-loaded TiO₂ photocatalysts and various porous materials were introduced to the photocatalytic reaction. The photochemical decomposition by irradiation of the liquid phase plasma without photocatalysts produced some hydrogen evolution with the degradation of acetaldehyde, which was attributed to the decomposition of the reactant by active species generated by the irradiation of liquid phase plasma. The Ni loading on TiO₂ brought out an enhancement of acetaldehyde degradation and hydrogen evolution. In the photocatalysis of acetaldehyde-contained wastewater using the liquid phase plasma, hydrogen evolution was accelerated due to the additional hydrogen production by the photocatalytic decomposition of acetaldehyde. The porous materials could be used as an effective photocatalytic support. MCM-41 mesoporous material has acted as a highly efficient photocatalytic support to the TiO₂ photocatalyst.     

N-Cdots-decorated TiO2(B)/anatase microspheres with high photocatalytic performance in visible light

Nitrogen-doped carbon dots (N-Cdots) with enhanced absorption in visible light region were combined with TiO₂(B)/anatase (TiO₂(A + B)) microspheres consist of nanosheets via a one-step synthesis. The successful connection of N-Cdots and TiO₂ substrate was confirmed by the appearance of new Ti–O–C bond. The degradation rate of Rhodamine B (RhB) for N-Cdots@TiO₂(B)/anatase was improved to seven times higher than that of initial TiO₂(B) microspheres under full spectrum illumination. N-Cdots@TiO₂(B)/anatase photocatalyst also exhibited high photocatalytic ability under visible light irradiation. The possible mechanism was proposed in two irradiation conditions. N-Cdots act as a semiconductor to generate electrons and holes. The electrons were transferred to the conduction band of TiO₂(B) and anatase, which improved the visible light utilization efficiency. Meanwhile, the heterophase structure of TiO₂(A + B) substrate restrained the recombination of electron-hole pairs. It is the synergistic effect of heterophase and N-Cdots that enhanced the photocatalytic performance.     

Hierarchical TiO2 spheroids decorated g-C3N4 nanocomposite for solar driven hydrogen production and water depollution

A novel hierarchical TiO₂ spheroids embellished with g-C₃N₄ nanosheets has been successfully developed via thermal condensation process for efficient solar-driven hydrogen evolution and water depollution photocatalyst. The photocatalytic behaviour of the as-prepared nanocomposite is experimented in water splitting and organic pollutant degradation under solar light irradiation. The optimal ratio of TiO₂ spheroids with g-C₃N₄ in the nanocomposite was found to be 1:10 and the resulting composite exhibits excellent photocatalytic hydrogen production of about 286 μmol h^?1g^?1, which is a factor of 3.4 and 2.3 times higher than that of pure TiO₂ and g-C₃N₄, respectively. The outstanding photocatalytic performance in this composite could be ascribed as an efficient electron-hole pair's separation and interfacial contact between TiO₂ spheroids with g-C₃N₄ nanosheets in the formed TiO₂/g-C₃N₄ nanocomposite. This work provide new insight for constructing an efficient Z-scheme TiO₂/g-C₃N₄ nanocomposites for solar light photocatlyst towards solar energy conversion, solar fuels and other environmental applications.     

Preparation of rGO/FeMoO4 as high-performance photocatalyst for degradation of malachite green,phenol and H2 evolution under natural sunlight

FeMoO₄ and rGO/FeMoO₄ nanocomposites were successfully prepared by a facile hydrothermal method. The XRD results confirmed that the FeMoO₄ has a monometallic β-FeMoO₄ crystalline phase while the rGO/FeMoO₄ showed both monometallic α- and β-FeMoO₄ phases where β-FeMoO₄ is the predominant phase. The reduction of graphene oxide (GO) to reduced graphene oxide (rGO) was performed without using any chemical reductions. UV–Vis results showed that the visible light absorption and band gap energy were enhanced after the addition of rGO. The prepared samples were successfully applied for degradation of malachite green (MG) and phenol (Ph) and for H₂ evolution under natural solar light irradiation. All the nanocomposites showed higher photocatalytic activities compared with pure FeMoO₄ photocatalyst, and the 10%rGO/FeMoO₄ gave the highest photodegradation performance for MG and Ph and for H₂ evolution. The photodegradation results revealed that the rGO content played the crucial factor in the photodegradation of MG and Ph, and H₂ evolution. The mineralization (TOC), photodegradation mechanism and degradation kinetics of MG and Ph were discussed.     

Parallel-plate solar photocatalytic reactor for air purification: Semi-empirical correlation, modeling, and optimization

This study focused on modeling and optimization of a photoreactor packed with parallel glass plates coated with sol–gel TiO₂ thin films on both sides. The photoreactor design has great potential for solar photocatalytic air purification. Borosilicate glass substrate was selected because its high transmissivity facilitated the transmission and distribution of exterior solar radiation onto interior immobilized photocatalyst. Flat-plate configuration was adopted because a TiO₂-coated plate could be easily set up for effective ion implantation treatment to extend the activating spectral range from UV to visible light for a higher solar photonic efficiency. In the analytical study of this research, a semi-empirical correlation model was formulated for prediction of the photoreactor performance. The correlation coefficients were obtained based on the results of photocatalytic air purification experiments conducted. Additional experimental tests were carried out for validation of the model. In the photoreactor design optimization analysis, the semi-empirical correlation model was used as an optimizer to determine the number of parallel TiO₂-coated plates needed for efficient photocatalytic air purification. It was found that the optimal number of plates was dependent of the incident irradiance. The modeling and optimization methods developed for solar photocatalytic air purification are equally applicable for solar photocatalytic water purification.     

Mesoporous carbon/graphitic carbon nitride spheres for photocatalytic H2 evolution under solar light irradiation

Herein, two different photocatalytic composites based on ordered (OCS) and disordered (DCS) mesoporous hollow carbon spheres and graphitic carbon nitride (gCN) have been successfully fabricated through facile acid treatment. The influence of carbon shell morphology of the spheres on gCN loading and photocatalytic H₂ production under simulated solar light irradiation has been revealed. The amount of evolved H₂ was ~6.2 (OCS/gCN) and ~5.3 (DCS/gCN) times higher in comparison to pristine gCN. It was found that graphitic carbon nitride was much more homogenously supported onto ordered mesoporous carbon spheres than disordered ones. The deposition of gCN onto ordered carbon spheres was found to be more efficient to increase carrier concentration, enhance photogenerated charge carrier transport and separation. It is assigned to the formation of the graphitic carbon nitride/carbon heterojunction facilitating the contact surface between the two phases of hybrid. Therefore, via tuning of the morphology of carbon shell being a host for gCN it was possible to find more promising candidate as a photocatalyst in H₂ production under solar light irradiation.