In the future, solar energy, along with other renewable resources, could play a key role in mass production of fine chemicals. It could also potentially solve environmental problems, as demonstrated by recent developments in the use of solar energy, such as solar photocatalysis. The solar photocatalytic technology has been demonstrated to be effective for: • Treating groundwater, drinking water, industrial wastewater, and air and soil pollution, • Water disinfection, and • Industrial production of fine chemicals. This report summarizes the current status of solar photocatalysis and identifies future opportunities for research and industry in this field, including recent relevant bibliography. The main commercial solar photocatalytic applications are described, included the technologies based on sunlight for antifogging and self-cleaning of coating materials, glass, and concrete. An overview of several different solar photoreactors and the main operating process parameters are also provided. For the estimation of capital costs, it is suggested the use of appropriate “figures of merit”. The present review would be of interest for researchers, technologists, engineers, and industrialists.

Solar photocatalysis: Materials, reactors, some commercial, and pre-industrialized applications. A comprehensive approach

Water purification for human use, ecosystem management, agriculture, and industry is emerging as a leading global priority. Access to sufficient clean water ultimately requires improvements over the current state of water filtration technology. Membrane technologies for water purification have been actively pursued for decades, but with recent innovation of both analytical and fabrication tools, more advanced membrane technologies are surfacing. Here, we review the design, development, and application of new membrane materials, fabrication methods for controlling the filtration size regime, analytical tools for performance testing, and molecular modeling for transport and separation. Membrane chemical stability, fouling, and environmental impact as open questions are also presented.

Membrane materials for water purification: design, development, and application

Important challenges in the global water situation, mainly resulting from worldwide population growth and climate change, require novel innovative water technologies in order to ensure a supply of drinking water and reduce global water pollution. Against this background, the adaptation of highly advanced nanotechnology to traditional process engineering offers new opportunities in technological developments for advanced water and wastewater technology processes. Here, an overview of recent advances in nanotechnologies for water and wastewater treatment processes is provided, including nanobased materials, such as nanoadsorbents, nanometals, nanomembranes, and photocatalysts. The beneficial properties of these materials as well as technical barriers when compared with conventional processes are reported. The state of commercialization is presented and an outlook on further research opportunities is given for each type of nanobased material and process. In addition to the promising technological enhancements, the limitations of nanotechnology for water applications, such as laws and regulations as well as potential health risks, are summarized. The legal framework according to nanoengineered materials and processes that are used for water and wastewater treatment is considered for European countries and for the USA.

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Innovations in nanotechnology for water treatment.

Green synthesis of TiO2 nanoparticles using leaf extract of Jatropha curcas L. for photocatalytic degradation of tannery wastewater.

Intensive research work is being undertaken globally to effectively use the process of photocatalysis for the degradation of organic pollutants from industrial effluents. For the same, TiO2 has been extensively explored, which however, has a limitation of being able to utilise the UV spectrum only, due to its high band gap property. Since a substantial percentage of the solar spectrum is visible light, it is imperative that for an effective and versatile utilisation of the incident solar energy, visible light active photocatalysts, having a relatively smaller band gap are developed. Smaller band gap, however, often results in rapid recombination and conversion of photonic energy into non-usable heat. This article is a review of the science behind the performance of visible/solar light active photocatalysts. The first part includes the fundamentals of photocatalysis, including thermodynamics, reaction kinetics and recombination. The second part reviews the visible/solar light active photocatalytic materials as well as the significant research efforts made so far in the exploration of possible mechanisms of photoexcitation and remedies for minimization of recombination. Finally, an operational overview is provided which is helpful in assessing the influence of key parameters on the photocatalytic activity. This review presents a single point reference for a comparative study and ready assimilation of the basics and new directions in photocatalysis, thus making it more conducive to further research and active commercialisation.

Visible/solar light active photocatalysts for organic effluent treatment: Fundamentals, mechanisms and parametric review

Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.

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Shaji Varghese

Papers

Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates