Semiconductor heterojunctions are pivotal in determining the overall photocatalytic efficiency. This review explores recent advances in diverse heterojunction types, charge transfer mechanisms and materials.

It is a subject of exploration whether the phase pure anatase or rutile TiO₂ or the band alignment due to the heterojunctions in the two polymorphs of TiO₂ plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO₂ have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO₂ has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO₂. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.

Enzyme-embedded polymer degradation was reported to be an attractive alternative approach to the conventional surface pouring method for efficient degradation of polymers using fungal-derived enzyme Candida antarctica lipase B. Despite the enormous potential, this approach is still in its infancy. In the present study, a probiotic lipase obtained from Lactobacillus plantarum has been employed for the first time to study the enzyme-embedded polymer degradation approach using poly(ε-caprolactone) (PCL) as the semicrystalline polymer candidate. PCL films embedded with 2 to 8 wt % lipase are studied under static conditions for their enzymatic degradation up to 8 days of incubation. Thermogravimetric analyses (TGA) have shown a clear trend in decreasing thermal stability of the polymer with increasing lipase content and number of incubation days. Differential thermal analyses have revealed that the percentage crystallinity of the leftover PCL films increases with progress in enzymatic degradation because of the efficient action of lipase over the amorphous regions of the films. Thus, the higher lipase loading in the PCL matrix and more number of incubation days have resulted in higher percentage crystallinity in the leftover PCL films, which has further been corroborated by X-ray diffraction analyses. In a similar line, higher percentage mass loss of the PCL films has been observed with increased enzyme loading and number of incubation days. Field emission scanning electron microscopy (FE-SEM) has been employed to follow the surface and cross-sectional morphologies of the polymer films, which has revealed micron-scale pores on the surface as well as a bulk polymer matrix with progress in enzymatic polymer degradation. Additionally, FE-SEM studies have revealed the efficient enzyme-catalyzed hydrolysis of the polymer matrix in a three-dimensional fashion, which is unique to this approach. In addition to the first-time utility of a probiotic lipase for the embedded polymer degradation approach, the present work provides insight into the PCL degradation under static and ambient temperature conditions with no replenishment of enzymes.