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With the fast development of industrialization and urbanization, large amounts of organic pollutants are released into the natural environment. The efficient elimination of organic pollutants is thereby crucial for environmental pollution treatment and human health. In the last decades, photocatalytic degradation of persistent organic pollutants has attracted multidisciplinary interest because of its simple operation on a large scale. However, the whole processes for the photocatalytic degradation of organic pollutants are still unclear. In this perspective, the contribution of reactive species, the contribution of photocatalysts, the analysis of intermediate products, the charge transfer and fast carrier recombination are discussed on biochar-based photocatalysts.

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil. Graphical Abstract

In order to improve the efficiency of biotransformation of saponins in Dioscorea zingiberensis to diosgenin, a new enzymatic model was developed to investigate the mechanism of the metabolic systems. Four main saponin hydrolases (E1, E2, E3 and E4) were purified from Trichoderma reesei. Using progracillin as substrate, the enzymatic hydrolysis experiments with E1, E2, E3 and E4 were carried out respectively. Saponin concentrations during each biotransformation reaction were constructed with a kinetic model consisting of a few Michaelis-Menten equations. During biotransformation, C-26 glycoside and C-3 terminal glycoside were cleaved sequentially from saponins by E1, E2, E3 and E4. Then C-3 terminal rhamnoside and C-3 glycoside were released from the aglycone stepwisely by E2 and E3, to yield diosgenin. E2 and E3 were the key enzymes in the system, and cleavage of the C-3 glycoside from saponins was the rate-limiting step in the biotransformation process. The proposed enzymatic model might be used to analyze the mechanism for biotransformation of saponins to diosgenin.