A review on preparation, surface enhancement and adsorption mechanism of biochar‐supported nano zero‐valent iron adsorbent for hazardous heavy metals

Abstract

Heavy metal pollution of water is a global concern, which adversely affects human health because of its resistance to biodegradation and thus its transmission in the food chain via bioaccumulation. Nano zerovalent iron (nZVI) is very effective for the removal of heavy metals and is cost effective in terms of production. However, the main problems of nZVI are agglomeration and ease of oxidation. Several stabilization materials have been implemented to limit the aggregation of nZVI, such as silica, activated carbon and biochar. In comparison, as a support material, biochar possesses a large surface area, high stability and strong adsorption capacity, as well as being obtainable from various types of materials. Thus, this work aims to establish the opportunities available on the use of biochar-supported nZVI in utilizing its ability to stabilize and immobilize the nZVI. This review also reports the preparation, modification and surface enhancement of biochar, nZVI and biochar-nZVI for practical use as adsorbents. This review shows that modifications of the nZVI surface can help in their stabilization and reduction of aggregation. Additionally, this review is able to increase one's understanding of heavy metal sorption behavior by biochar-supported nZVI as it is the important as heavy metal sorption is driven based on biochar-nZVI type and heavy metal species which involve numerous mechanisms, including physical binding, complexation, ion exchange, surface precipitation and electrostatic interactions. Furthermore, this research reviews the adsorption parameters, including the crucial adsorption mechanism of heavy metals onto biochar-nZVI; the reusability of the biochar-nZVI is also discussed in this work.

Pb(II) Removal from Aqueous Solutions by Adsorption on Stabilized Zero-Valent Iron Nanoparticles—A Green Approach

“…As a result of its large specific surface area, stable microporous structure, wide availability, affordability, great adsorption capacity, and compatibility with the environment, biomass-derived activated carbon (BAC) can be an appropriate support material for nZVFe particles. Consequently, in addition to stabilizing iron NPs by providing more interaction between NPs and Pb ions, it will increase the absorption capacity of the resulting composite [60,61]. On the other hand, rice is the primary crop and staple food for more than half of the world's population.…”

Immobilized Nanomaterials for Environmental Applications

“…In the same way, BC has emerged as a low-cost alternative for metal NP immobilization [ 101 ], including the environmental and economic benefits associated with the use of biomass waste materials instead of non-renewable sources for AC production [ 102 ]. The intensive use of BC as a host material for NP immobilization is reflected in a recent review that summarized its performance as an nZVI support for heavy metal adsorption [ 103 ], and another focused on the preparation, environmental application, and prospect of BC-supported metal NPs [ 101 ]. Many sources for BC production, such as wood, coconut shell, corn straw, rice husk, nutshell, and peach stone, among others, have been explored, mainly based on their carbon content, abundance, inherent environmental issues, and mechanical properties [ 99 , 101 , 104 ].…”

“…NMs, including metal NPs such as Fe, Cu, Au, Pt, Pd, Ru, Ag, Co, and Ni, are the subject of great scientific and economic interest for oil-refining, chemical-manufacturing, and environmental catalysis applications [ 96 ]. In adsorption processes for the removal of heavy metals from contaminated water, iron and iron oxide NPs, immobilized in carbonaceous matrixes, have been extensively described, such as Cd 2+ , Cu 2+ , Ni 2+ , Co 2+ , Cr 6+ , Pb 2+ , As 3+ , and Hg 2+ [ 103 , 113 ]. Additionally, the inclusion of metal NPs, such as MgO, CaO, Fe 2 O 3 , Al 2 O 3 , Fe 0 , and Ag 0 , on carbon nanocomposites can successfully improve the ligand-binding density by increasing the positive charge, allowing the higher removal of inorganic compounds than raw carbon materials [ 101 ].…”

Nano Modifications of Biochar to Enhance Heavy Metal Adsorption from Wastewaters: A Review

“…Biochar can be modified by loading it with organic functional groups, minerals such as hematite (γ-Fe 2 O 3 ) and reductants; and by activating it with an alkali solution to enhance its sorption capacity. Chemically modified biochar usually exhibits enhanced adsorption capacity as compared to the raw biochar. , Surface modification of biochar with nanomaterials is a promising strategy affecting its sorption capacity for contaminant removal. , Nanomaterials exhibit higher surface-to-volume ratio compared to the bulk materials which help in improving functional groups, surface active sites, pore size, and catalytic degradation ability of biochar. Therefore, nanomaterials have properties that endow these materials to exhibit both chemical reduction and catalysis reactions that can help to mitigate the pollutants or contaminants, i.e., nanoremediation.…”

“… 3 , 33 Surface modification of biochar with nanomaterials is a promising strategy affecting its sorption capacity for contaminant removal. 34 , 35 Nanomaterials exhibit higher surface-to-volume ratio compared to the bulk materials which help in improving functional groups, surface active sites, pore size, and catalytic degradation ability of biochar. Therefore, nanomaterials have properties that endow these materials to exhibit both chemical reduction and catalysis reactions that can help to mitigate the pollutants or contaminants, i.e., nanoremediation.…”