Review of organic and inorganic pollutants removal by biochar and biochar-based composites

Biochar (2021) 3:255–281 https://doi.org/10.1007/s42773-021-00101-6 REVIEW Review of organic and inorganic pollutants removal by biochar and biochar‑based composites Liping Liang1 · Fenfen Xi1 · Weishou Tan1 · Xu Meng2 · Baowei Hu1 · Xiangke Wang1 Received: 22 January 2021 / Accepted: 11 May 2021 / Published online: 7 July 2021 © The Author(s) 2021 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. Keywords Biochar magnetic composites · Nanometallic oxide/hydroxide biochar composites · Biochar based 2D membrane · 3D biochar-based macrostructures · Biological toxicity 1 Introduction Along with the rapid growth of industry and economy, water pollution has seriously endangered the environment and human health. Most of the pollutants in aqueous solutions come from chemical pollution, including heavy metals (Cu, Cr, Pb, Ni, etc.) (Islam et al. 2015), metalloids (Se, As, etc.) (Bender et al. 1995) and organic pollutants (dyes, antibiotics, etc.) (Hao et al. 2021; Schwarzenbach et al. 2010; Yao et al. 2020). Heavy metals are not biodegradable and tend to accumulate in living organisms through the food chain. Organic pollutants, because of high persistence, difficult * Baowei Hu * Xiangke Wang 1 College of Life Science, Shaoxing University, Shaoxing 312000, People’s Republic of China 2 College of Textile and Garment, Shaoxing University, Shaoxing 312000, People’s Republic of China removal, easy transfer, and extreme toxicity pose a serious threat to human health (Houde et al. 2008; Liu et al. 2021a, b). Facing severe water pollution, there is urgent need to find cost-effective technologies based on low-cost materials. Among numerous separation technologies for contaminants in wastewater treatment, adsorption is preferred owing to its relatively high efficiency, low cost, and easy operation (Huggins et al. 2016). Recenrly, BC has become a new sorbent for its superior properties, such as eco-friendliness, abundant in functional groups and inorganic mineral species, containing micro and/or meso-porous structures and high adsorption capacity, which were widely employed to remove the contaminants from wastewater (Shaheen et al. 2019; Hu et al. 2020). Moreover, BC’s feedstocks are stem from solid waste, agricultural biomass, animal litters, and the preparation does not need activation, which means BC has a great potential in environmental remediation (Liu and Zhang 2011). Nonetheless, there are still some limitations of the pristine BC to selectively adsorb high concentration contaminants (Ma et al. 2014). To overcome this shortage, the BC-based composite materials were obtained by further 13 Vol.:(0123456789) 256 activation and modification to improve the specific surface area, pore structure, and surface functional groups (Zhang et al. 2015; Xue et al. 2012). BC-based composite materials can be selectively designed or produced for the target pollutants by adding functional materials, magnetic substances, and nanoparticles. Those composite materials are rich in functional groups that can make up the shortage of pristine BCs in environmental remediation. As is known to all, the contaminant’s removal efficiency and mechanisms of BC and BC-based composite materials were related to the mineral content, ionic content, organic functional groups, etc. (Shaheen et al. 2019). However, the performances of BC and BC-based composite materials were also related to biomass, reaction parameters, etc. For example, the pH value of BC prepared at a higher temperature was relatively high, while BC prepared under lower temperature contained more toxic substances, such as polycyclic aromatic hydrocarbons (PAH), polychlorinated dibenzo dioxins (PCDD), and polychlorinated dibenzo furans (PCDF). And BC stemming from animal manure was rich in ash. Currently, a variety of studies confirmed that BC-based composites could significantly improve the performance of contaminants removal. For instance, Ioannou et al. (2019) reported that 100% U(VI) from aqueous solutions could be removed by M nO2-BC and the maximum adsorption capacity (qm) reached 904 mg/g. Similarly, Khataee et al. (2017) synthesized TiO2-BC, which enhanced the sonocatalytic degradation efficiency of Reactive Blue 69 (RB69) from 63.8 to 98.1%, and the removal efficiency was still 92.1% after five successive processes in this systems. So, it was necessary to develop some new strategies for new BC-based materials such as 2D membranes, 3D carbonaceous hydrogels/aerogels or immobilized microorganisms on it to better remove contaminants. However, applications of BC particles and BC-based composites inevitably release fine particles into the environment which may cause biological toxicity and damage human health (Lu et al. 2020; Lian and XIng 2017; Zhang et al. 2019b). For example, the addition of rice straw BC into contaminated soil reduced the bioavailability of Pb; − SO2− meanwhile, DOC, PO2− 4 Cl , and 4 were released. Other researchers found that under oxidizing conditions, the application of BC in soil remediation increased the concentration of As and Co in the dissolved phase. All of these toxic chemicals may transfer into food chains and cause toxic or side effects on human and environmental health (El-Naggar et al. 2019b, c; Rinklebe et al. 2020). Besides, BC-treated soil may change the pH value, which will have an impact on organisms (El-Naggar et al. 2018; Kookana et al. 2011). In this paper, we summarized the physicochemical properties of biochar, the preparation method, the performance, and the mechanisms of BC,and BC-based compo (...truncated)