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

Biochar (BC) has exhibited a great potential to remove water contaminants due to its wide availability of raw materials, high surface area, developed pore structure, and low cost. However, the application of BC for water remediation has many limitations. Driven by the intense desire of overcoming unfavorable factors, a growing number of researchers have carried out to produce BC-based composite materials, which not only improved the physicochemical properties of BC, but also obtained a new composite material which combined the advantages of BC and other materials. This article reviewed previous researches on BC and BC-based composite materials, and discussed in terms of the preparation methods, the physicochemical properties, the performance of contaminant removal, and underlying adsorption mechanisms. Then the recent research progress in the removal of inorganic and organic contaminants by BC and BC-based materials was also systematically reviewed. Although BC-based composite materials have shown high performance in inorganic or organic pollutants removal, the potential risks (such as stability and biological toxicity) still need to be noticed and further study. At the end of this review, future prospects for the synthesis and application of BC and BC-based materials were proposed. This review will help the new researchers systematically understand the research progress of BC and BC-based composite materials in environmental remediation.

Graphitic carbon nitride (g-C₃N₄), with a moderate band gap (∼2.7 eV), high chemical and thermal stability, has been the hotspot in environmental photocatalysis. However, its performance is still unsatisfactory because of insufficient absorption of visible light, poor surface area, low electronic conductivity and high recombination rate of photogenerated electron-hole pairs. The modification of g-C₃N₄ could overcome these problems to improve photocatalytic properties. Among various modification strategies, element doping is an efficient and simple strategy for adjusting electronic structure and accelerating photocatalytic performance. This review focused on the progress and trends of designing typical, cost-effective element-doped carbonized nitrogen and its degradation of environmental organic pollutants. The heterogeneous catalytic mechanisms of g-C₃N₄-based photocatalysts for organic pollutants degradation have been explicated in detail. The increased photocatalytic performance of g-C₃N₄ by doping various elements was discussed clearly. The surface properties, catalyst performance and pollution management of various elements-doped g-C₃N₄ were compared and subsequently analyzed some dilemmas and application strategies for g-C₃N₄ development in depth. This review can light up a new way and afforded valuable clues to design g-C₃N₄ doping elements to exploit more effective photocatalyts for real applications in environmental pollution management.