Volume 38, Issue 6

The threat of dye contamination has achieved an unsurpassed abnormal state lately due to their massive consumption in several enterprises including textile, leather, cosmetic, plastic, and paper industries. This review focuses on the integrations of various advanced oxidation processes (AOPs), such as Fenton, photocatalysis, and ozonation, with biodegradation for the treatment of textile azo dyes. Such integrations have been explored lately by researchers to bring down the processing cost and improve the degree of mineralization of the treated dyeing wastewater. The review refers to the basic mechanisms, the influence of various process parameters, outcomes of recent works, and future research directions. All the three AOPs, independently, demonstrated substantial color reduction of 54–100%. The ozonation process, stand-alone, showed the most efficient decolorization (of 88–100%) consistently in all reviewed research works. In contrast, all three AOPs independently offered varied and inadequate COD reduction in the range of 16–80%. The AOPs, after getting integrated with biodegradation, yielded an additional reduction (of 11–70%) in the COD-levels and (of 16–80%) in the TOC-levels. Further, the integration of AOPs with biodegradation has potential to significantly reduce the treatment costs. The review suggests further research efforts in the direction of sequencing chemical and biological routes such that their synergistic utilization yield complete detoxification of the textile azo dyes economically at large-scale.

Titanium dioxide (TiO 2 ) is commonly used as a photocatalyst in the removal of organic pollutants. However, weaknesses of TiO 2 such as fast charge recombination and low visible light usage limit its industrial application. Furthermore, photocatalysts that are lost during the treatment of pollutants create the problem of secondary pollutants. Electrospun-based TiO 2 fiber is a promising alternative to immobilize TiO 2 and to improve its performance in photodegradation. Some strategies have been employed in fabricating the photocatalytic fibers by producing hollow fibers, porous fibers, composite TiO 2 with magnetic materials, graphene oxide, as well as doping TiO 2 with metal. The modification of TiO 2 can improve the absorption of TiO 2 to the visible light area, act as an electron acceptor, provide large surface area, and promote the phase transformation of TiO 2 . The improvement of TiO 2 properties can enhance carrier transfer rate which reduces the recombination and promotes the generation of radicals that potentially degrade organic pollutants. The recyclability of fibers, calcination effect, photocatalytic reactors used, operation parameters involved in photodegradation as well as the commercialization potential of TiO 2 fibers are also discussed in this review.

Concentration solar power (CSP) systems convert solar radiation to heat and use heat engines to convert the heat to electricity. The solar receiver over which the solar radiation is concentrated and converted to heat is the most important part of the CSP. To attain maximum efficiency, the receiver in the CSP systems needs to be coated with an efficient selective solar absorber coating. In recent years, a lot of research has been focused on solar selective coatings. This has resulted in the synthesis of novel coatings that have high thermal and chemical stability, long term durability, and excellent solar selectivity making them suitable for solar thermal applications. This report reviews various solar selective coatings based on transition metals and their compounds. Various failure mechanisms are discussed in detail along with suggested prevention methods. Several thermal stability and durability tests are reported with their benefits and limitations. The effect of long-term durability on the levelized cost of coating is also discussed. Finally, we list some excellent systems and explore different ways of improving the thermal stability for SSCs, thus providing a reference for the design and optimization of new SSCs.

Responsive molecularly imprinted microgels (MIGs) have gained a lot of interest due to their responsive specificity and selectivity for target compounds. Study on MIGs is rapidly increasing due to their quick responsive behavior in various stimuli like pH and temperature. MIGs show unique property of morphology control on in-situ synthesis of nanoparticles in response of variation in reactant concentration. Literature related to synthesis, parameters, characterization, applications and prospects of MIGs are critically reviewed here. Range of templates, monomers, initiators and crosslinkers are summarized for designing of desired MIGs. This review article describes effect of variation in reactants combination and composition on morphology, imprinting factor and percentage yield of MIGs. Hydrolysis of similar templates using MIGs is also described. Relation between percentage hydrolysis and hydrolysis time of targets at different temperatures and template:monomer ratio is also analyzed. Possible imprinting modes of ionic/non-ionic templates and its series are also generalized on the basis of previous literature. MIGs are investigated as efficient anchoring vehicles for adsorption, catalysis, bio-sensing, drug delivery, inhibition and detection.

The work that has been carried out on microwave irradiation applied in catalyst preparation for drying, calcination or postsynthesis methods, and as a heating source for the Fischer–Tropsch reaction has been reviewed. It has been found that microwave irradiation can, in some cases, greatly enhance the performance of heterogeneous catalyst systems for Fischer–Tropsch synthesis. We have also summarized the advantages and drawbacks of using microwave irradiation in Fischer–Tropsch catalyst preparation and postsynthesis, and identified opportunities for future investigation.