A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Rashid M. S., Liu G., Yousaf B., Hamid Y., Rehman A., Arif M., ...More

ENVIRONMENTAL POLLUTION, vol.315, 2022 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Review
  • Volume: 315
  • Publication Date: 2022
  • Doi Number: 10.1016/j.envpol.2022.120335
  • Journal Name: ENVIRONMENTAL POLLUTION
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, PASCAL, Aerospace Database, Aqualine, Aquatic Science & Fisheries Abstracts (ASFA), BIOSIS, Biotechnology Research Abstracts, CAB Abstracts, Chemical Abstracts Core, Chimica, Communication Abstracts, Compendex, EMBASE, Environment Index, Food Science & Technology Abstracts, Geobase, Greenfile, MEDLINE, Metadex, Pollution Abstracts, Veterinary Science Database, Civil Engineering Abstracts
  • Keywords: Biochar, Free radicals, Heavy metals, Toxicity, Environmental fate, PERSISTENT FREE-RADICALS, HYDROGEN-PEROXIDE ACTIVATION, ZERO-VALENT IRON, CONTAMINATED SOIL, HEAVY-METALS, RICE STRAW, ELECTRON-DONOR, CARBON BIOCHAR, REMEDIATION, NICKEL
  • Middle East Technical University Affiliated: Yes

Abstract

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating poten-tial may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, py-rolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feed-stocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the func-tion of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.