Microwave assisted photocatalytic degradation of pentachlorophenol in aqueous TiO2 nanotubes suspension

An overview on non-spherical semiconductors for heterogeneous photocatalytic degradation of organic water contaminants

Because of their carcinogenicity and mutagenicity, the elimination of organic contaminants from surface and subsurface water is a subject of environmental significance. Conventional water decontamination approaches such as membrane separation, ultrafiltration, adsorption, reverse osmosis, coagulation, etc., have relatively higher operating costs and can generate highly toxic secondary contaminants. On the other hand, heterogeneous photocatalysis, an advanced oxidation process (AOP), is considered a clean and cost-effective process for organic pollutants degradation. Owing to their distinctive structure and physicochemical properties non-spherical semiconductors have gained considerable limelight in the photocatalytic degradation of organic contaminants. The current review briefly introduces a wide range of organic water contaminants. Recent advances in non-spherical semiconductor assembly and their photocatalytic degradation applications are highlighted. The underlying mechanism, fundamentals of photocatalytic reactions, and the factors affecting the degradation performance are also alluded including the current challenges and future research perspectives.

Enhanced the photoelectrocatalytic performance of TiO2 nanotube arrays by the synergistic sensitization of Ag-AgBr nanospheres

Ag-AgBr nanospheres were synthesized on the tubular surface of TiO₂ nanotube arrays (TiO₂ NTA/Ag-AgBr) by the one-pot hydrothermal deposition strategy using cetyltrimethyl ammonium bromide (CTAB) as bromine source and morphology controlling agent. The results showed that the TiO₂ NTA/Ag-AgBr (0.025) prepared with 0.025 g CTAB had the uniform particle distribution, high visible light absorption, photoelectric conversion activity and photoelectrocatalytic (PEC) removal of organic dyes and heavy metal ions. The high photocatalytic decomposition of organic pollutants in waste water was attributed to the synergistic effect of Ag-AgBr nanospheres with the strong visible light response and effective separation of electron-hole pairs. The active group and photocatalytic mechanism for the rapid pollutant removal were systematically explored. This work will open the window of TiO₂ NTA based photoelectrodes for the applications in solar energy conversion and dyeing waste water purification.

Emerging trends in photodegradation of petrochemical wastes: a review

Various human activities like mining and extraction of mineral oils have been used for the modernization of society and well-beings. However, the by-products such as petrochemical wastes generated from such industries are carcinogenic and toxic, which had increased environmental pollution and risks to human health several folds. Various methods such as physical, chemical and biological methods have been used to degrade these pollutants from wastewater. Advance oxidation processes (AOPs) are evolving techniques for efficient sequestration of chemically stable and less biodegradable organic pollutants. In the present review, photocatalytic degradation of petrochemical wastes containing monoaromatic and poly-aromatic hydrocarbons has been studied using various heterogeneous photocatalysts (such as TiO₂, ZnO and CdS. The present article seeks to offer a scientific and technical overview of the current trend in the use of the photocatalyst for remediation and degradation of petrochemical waste depending upon the recent advances in photodegradation of petrochemical research using bibliometric analysis. We further outlined the effect of various heterogeneous catalysts and their ecotoxicity, various degradation pathways of petrochemical wastes, the key regulatory parameters and the reactors used. A critical analysis of the available literature revealed that TiO₂ is widely reported in the degradation processes along with other semiconductors/nanomaterials in visible and UV light irradiation. Further, various degradation studies have been carried out at laboratory scale in the presence of UV light. However, further elaborative research is needed for successful application of the laboratory scale techniques to pilot-scale operation and to develop environmental friendly catalysts which support the sustainable treatment technology with the "zero concept" of industrial wastewater. Nevertheless, there is a need to develop more effective methods which consume less energy and are more efficient in pilot scale for the demineralization of pollutant.

Microwaves and their coupling to advanced oxidation processes: enhanced performance in pollutants degradation

This review assesses microwaves (MW) coupled to advanced oxidation processes (AOPs) for pollutants degradation, as well as the basic theory and mechanisms of MW dielectric heating. We addressed the following couplings: MW/H2O2, MW/UV/H2O2, MW/Fenton, MW/US, and MW/UV/TiO2, as well as few studies that tested alternative oxidants and catalysts. Microwave Discharge Electrodeless Lamps (MDELs) are being extensively used with great advantages over ballasts. In their degradation studies, researchers generally employed domestic ovens with minor adaptations. Non-thermal effects and synergies between UV and MW radiation play an important role in the processes. Published papers so far report degradation enhancements between 30 and 1,300%. Unfortunately, how microwaves enhance pollutants is still obscure and real wastewaters scarcely studied. Based on the results surveyed in the literature, MW/AOPs are promising alternatives for treating/remediating environmental pollutants, whenever one considers high degradation yields, short reaction times, and small costs.

Photodegradation of crystal violet in TiO(2) suspensions using UV-vis irradiation from two microwave-powered electrodeless discharge lamps (EDL(-2)): products, mechanism and feasibility

Aqueous crystal violet (CV) solutions containing P25-TiO(2) photocatalyst were irradiated with ultraviolet-visible (UV-vis) light from two microwave-powered electrodeless discharge lamps (EDL(-2)). The results demonstrated that approximately 94.4% of CV was effectively removed after 3 min of irradiation, with a pseudo-first order kinetic constant of 0.838 min(-1). According to 32 kinds of products, a five-step degradation pathway of CV was proposed. Further investigations showed that (1) three kinds of N-demethylated products and 4-dimethylaminobenzophenone (DLBP) were the main intermediates; (2) malachite green (MG) and leuco-crystal violet could not be generated by N-demethylation and phototransformation reactions, respectively; (3) bis(4-(dimethylamino)phenyl)methanone preferentially generated via decomposition of the conjugated structure of CV could be further N-demethylated into DLBP. Moreover, the unique degradation pathways of CV and MG were ascribed to the different substituents on the conjugated structures. Additionally, the cost and kinetic constant of different processes was also evaluated, and the results indicated the feasibility of this method for treatment of CV in field situations.

Enhanced photocatalysis on TiO2 nanotube arrays modified with molecularly imprinted TiO2 thin film

A molecularly imprinted TiO(2) film was constructed onto the surface of a TiO(2) nanotube (NT) array, getting a novel composite TiO(2) catalyst. Compared with unmodified TiO(2) NT and the non-imprinted film modified TiO(2) NT, the molecularly imprinted film modified TiO(2) NT not only exhibits a much higher adsorption capacity for the target contaminant but also shows an enhanced photocatalytic activity in degrading the target contaminant. Moreover, the molecularly imprinted inorganic semiconductor film is not degraded during photocatalysis, owing to its stable physicochemical properties which is superior to those of conventional molecularly imprinted organic polymer films.

Microwave-enhanced H2O2-based process for treating aqueous malachite green solutions: intermediates and degradation mechanism

This work was originally performed to compare H(2)O(2)-based degradation of aqueous malachite green (MG) under microwave (MW)-enhanced and conventional heating (CH)-enhanced conditions, with the whole reaction courses traced by UV-vis spectrophotometer. The results showed that the higher discoloration rates of MG were available during MW-enhanced process, implying that the special heating way of MW might be more benefit for the generation of hydroxyl radicals than that of CH. Furthermore, major intermediates were separated and identified by HPLC-ESI-MS and GC-MS techniques. On the basis of 53 intermediates, degradation mechanism was deduced as follows: firstly, N-de-methylation reactions. Secondly, adduction reactions. Thirdly, decomposition of conjugated structure reactions of MG. Fourthly, removal of benzene reactions. Finally, open-ring reactions. Additionally, results revealed that microwave-enhanced H(2)O(2)-based treatment had more advantages, such as higher degradation efficiency, and no removal of catalyst after treatment.

Microwave photocatalytic degradation of Rhodamine B using TiO2 supported on activated carbon: mechanism implication

The photocatalytic degradation of Rhodamine B (RhB) was carried out using TiO2 supported on activated carbon (TiO2-AC) under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET). In the process of microwave-enhanced photocatalysis (MPC), RhB (30 mg/L) was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates (N,N-diethyl-N'-ethyl-rhodamine (DER)), oxalic acid, malonic acid, succinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide.