This study is a critical approach to the widespread use of the first order form of the Langmuir–Hinshelwood (LH) equation for analyzing kinetics in heterogeneous photocatalytic processes. The ...different kinetic protocols analyzed have been applied to the results, published in the literature, of the photocatalytic degradation of phenol in an aqueous solution by a physical mixture of TiO2 particles and activated carbon (AC), the impact of which has been enormous over the last decade. It is commonly accepted that there is a strong synergy in this mixture due to the transfer of phenol from the activated carbon particles to TiO2. However, we found in this study that the apparent synergy between activated carbon and TiO2 particles arises from the erroneous use of the first order form of the LH equation. When applying the extended form of the LH equation, that includes the inhibitory effect of the phenol concentration, AC/TiO2 synergy should be disregarded. In this physical mixture the activated carbon merely alleviates the inhibitory effect of the phenol concentration by decreasing its initial value.
Schematic representation of MWCNT/WO3 composite. Display omitted
► Synthesis of multiwall carbon nanotube/tungsten oxide composite. ► Photocatalytic performance is enhanced by functionalized ...composite. ► MWCNTs acts as dispersing agent and controls the morphology of catalyst. ► Method has the potential as technology for environmental purification.
A composite of multi-walled carbon nanotube/tungsten oxide (MWCNT/WO3) has been successfully synthesized. The prepared composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The catalytic activity was investigated by rhodamine B degradation under solar irradiation. The influence of various degradation parameters such as solar illumination time, initial dye concentration, dosage and pH was investigated. It was found that the composite exhibits an enhanced photocatalytic activity as compared with WO3 and a mechanical mixture of MWCNTs and WO3. The enhancement in photocatalytic performance of the MWCNT/WO3 composite has been explained based on adsorption ability and electron transportation as a result of a strong interaction between WO3 and MWCNTs. Besides, MWCNTs acts as dispersing agent preventing WO3 from agglomerating during the catalytic process, providing a high active surface area of the catalyst. A reasonable mechanism for the enhanced reactivity was proposed.
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► ZnO/graphene-oxide (ZnO/GO) nanocomposite was synthesized via a facile chemical deposition route. ► The ZnO/GO nanocomposite exhibited remarkably enhanced visible-light-driven ...photocatalytic performance. ► The mechanism for photocatalytic degradation of methylene blue (MB) under visible light was discussed.
In this work, a high-performance photocatalyst of ZnO/graphene-oxide (ZnO/GO) nanocomposite was synthesized via a facile chemical deposition route and used for the photodegradation of organic dye from water under visible light. The nanocomposite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller N2 adsorption–desorption analysis, and UV–Vis diffusion reflectance spectroscopy. The ZnO/GO nanocomposite consisting of flower-like ZnO nanoparticles anchored on graphene-oxide sheets has a high surface area and hierarchical porosity, which is benefit to the adsorption and mass transfer of dye and oxygen species. For the photodegradation of organic dyes under visible light, ZnO/GO nanocomposite exhibited remarkably enhanced photocatalytic efficiency than graphene-oxide sheets and flower-like ZnO particles. Moreover, the photocatalytic efficiency of ZnO/GO nanocomposite could be further improved by annealing the product in N2 atmosphere. The outstanding photocatalytic performance was ascribed to the efficient photosensitized electron injection and repressed charge carriers recombination in the composite with GO as electron collector and transporter, thus leading to continuous generation of reactive oxygen species for the degradation of methylene blue.
In this review article the authors presented up to-date development on the application of adsorption in the removal of dyes from aqueous solution. This review article provides extensive literature ...information about dyes, its classification and toxicity, various treatment methods, and dye adsorption characteristics by various adsorbents. One of the objectives of this review article is to organise the scattered available information on various aspects on a wide range of potentially effective adsorbents in the removal of dyes. Therefore, an extensive list of various adsorbents such as natural materials, waste materials from industry, agricultural by-products, and biomass based activated carbon in the removal of various dyes has been compiled here. Dye bearing waste treatment by adsorption using low cost alternative adsorbent is a demanding area as it has double benefits i.e. water treatment and waste management. Further, activated carbon from biomass has the advantage of offering an effected low cost replacement for non-renewable coal based granular activated carbon provided that they have similar or better adsorption on efficiency. The effectiveness of various adsorbents under different physico-chemical process parameters and their comparative adsorption capacity towards dye adsorption has also been presented. This review paper also includes the affective adsorption factors of dye such as solution pH, initial dye concentration, adsorbent dosage, and temperature. The applicability of various adsorption kinetic models and isotherm models for dye removal by wide range of adsorbents is also reported here. Conclusions have been drawn from the literature reviewed and few suggestions for future research are proposed.
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•Extensive literature information about dye adsorption by wide range of adsorbents has been reviewed here.•Authors presented up-to-date development on the application of adsorption in the removal of dyes from their aqueous solution.•Various physico-chemical factors and mechanisms of dye adsorption have been critically analysed.
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