Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.

Monolithic silica aerogels with thermal conductivity as low as 0.036 W·(m·K)−1 and porosity as high as 97% were successfully prepared by ambient pressure drying through a multiple modification approach. This approach may replace the more costly and dangerous operation of supercritical drying. The tetraethoxysilane (TEOS)‐derived wet gel was made hydrophobic with multiple treatments of trimethylchlorosilane and dried under ambient pressure. The multiple treatments were found to be necessary to achieve sufficient modification of the wet gel for reduction in drying‐induced surface tension force to maintain product integrity and high porosity. Comparisons in nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy for surface bonding and contact angle measurement for hydrophobicity between the no, single, and multiple surface modification (MSM) samples were conducted to reveal the difference in the extent of the resulting surface modification. In conclusion, the MSM procedure reduced the volume shrinkage, increased the monolithicity and porosity, and lowered the thermal conductivity of the resulting aerogels.

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Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.