Insight into the chemically modified crop straw adsorbents for the enhanced removal of water contaminants: A review

Crop straws represent the major part of lignocellulosic wastes that mainly consist of three polymeric components, namely cellulose, hemicellulose, and lignin. These straws gain great attention owing to their low cost, abundance, renewability and functional groups enriched structure. However, the low adsorption capacity and the tendency to release soluble organic components into water limit the application of crop straws as adsorbents. Chemical modification has been efficiently adopted to avoid these drawbacks and improve the adsorption performance of raw straws. This article presents a review on the chemical modification of crop straws such as wheat, rice, corn, barley, and other straws. Commonly used modifications such as acid or alkali, esterification, etherification, surfactant, magnetic, etc. as well as their combination are discussed. The application of chemically modified crop straws as adsorbents for a variety of water contaminants, and their reuse after regeneration by different eluents are considered. The competitive adsorption behavior of multi-contaminant systems on these adsorbents is also included. The findings and future perspectives for the modification of crop straws and their utilization as adsorbents for water contaminants are finally summarized.