Innovative approaches to purify water using rice husk and rice husk ash-derived adsorbents: Recent advancement and mechanism

Rice husk (RH), an abundant and low-cost agricultural by-product in rice-producing countries, is commonly used as a fuel in boilers, generating rice husk ash (RHA) as a combustion by-product. Given their advantageous chemical compositions and surface characteristics, RH and RHA hold significant potential as precursors for synthesizing adsorbents aimed at water and wastewater remediation. This review provides a comprehensive overview of the synthetic pathways for converting RH and RHA into functional adsorbents including biochar, activated carbon, zeolites, and silica-based derivatives, alongside their applications in the remediation of various aquatic contaminants. The synthesis methods and characterization techniques for RH- and RHA-derived adsorbents are discussed, together with a critical evaluation of adsorption mechanisms, including isotherms and kinetics. Key factors governing adsorption performance toward heavy metals, dyes, and organic contaminants are systematically examined based on recent studies. Additionally, issues related to the regeneration and reusability of these adsorbents are addressed. The current literature collectively supports the promising role of RH and RHA as sustainable feedstocks for the development of low-cost adsorbents in aquatic pollution remediation.