生物炭简单丰富的来源，其丰富的孔隙结构以及独特的表面化学性质的特性，使其成为水处理应用中理想的可持续吸附剂。化学活化或制造复合材料修饰生物炭表面，可以进一步提高其吸附能力。层状双金属氢氧化物(LDHs)在水处理等各个领域的应用也得到了广泛关注。

The easy and abundant source, high porosity and unique surface chemistry properties make biochar an ideal and sustainable adsorbent for water treatment applications. The surface of biochar can be modified either by chemical activation or by making biochar-based composites, to further improve its adsorption capacity. Layered double hydroxides (LDHs) have also gained considerable attention owing to their applications in various fields including water treatment

 

LDHs与生物炭的协同效应在所得生物炭/LDH 复合材料的比表面积、表面官能团、结构异质性、稳定性等吸附特性方面表现出了显著的改善。本文着重评价了生物炭/LDHs复合材料在水处理中应用的最新进展，重点研究了各种污染物的吸附和催化降解。通过阐述吸附机理和再生能力，详细描述了生物炭/LDH 复合材料对各种有害污染物，即重金属、染料、阴离子和药物的吸附。最后，为未来的研究提出了展望，以确保生物炭/LDH 复合材料在水净化中的有效应用。

The synergistic effect of LDH with biochar exhibited significant improvement in specific surface area, surface functional groups, structure heterogeneity, stability, and adsorption characteristics of the resulting biochar/LDH composites. This paper critically evaluates the latest development in applications of biochar/LDH composites in water treatment with an emphasis on adsorption and catalytic degradation of various pollutants. The adsorption of various noxious contaminants, i.e., heavy metals, dyes, anions, and pharmaceuticals onto biochar/LDH composites are described in detail by elaborating the adsorption mechanism and regeneration ability. Finally, a roadmap is suggested for future research to assure the effective applications of biochar/LDH composites in water purification.

 

 

概述：生物炭/LDH 复合材料在水净化中的广泛应用

Overview: Biochar/LDH Composites for Water Purification Applications

（1）生物炭/LDHs复合材料去除阴离子

(1) Removal of Anions by Biochar/LDH Composites

生物炭/LDHs复合材料被广泛应用于去除水和废水中的磷酸盐和硝酸盐。如表1所示磷酸盐是使用生物炭/LDHs复合材料去除的研究最多的污染物。阴离子的吸附机制取决于阴离子的性质和生物炭/LDHs复合材料的物理化学特性。阴离子吸附最常见的机制是静电吸引、层间阴离子交换、表面络合、配体交换。

Biochar/LDH composites have been widely utilized for the removal of inorganic anions such as phosphate and nitrate from water and wastewater. As presented in Table 1, phosphate was the most studied pollutant removed by using biochar/LDH composites. The adsorption mechanism of anions was dependent on the nature of anions and physicochemical characteristics of biochar/LDH composites. The most common mechanisms for the adsorption of anions were the electrostatic attraction, interlayer anions exchange, surface complexation, ligand exchange, and memory effect.

 

（2）生物炭/LDH 复合材料去除重金属的研究

(2) Removal of Heavy Metals by Biochar/LDH Composites

各种生物炭/LDHs复合材料也被广泛报道可以有效去除重金属。与其他改性生物炭相比，高孔隙度和大量官能团和金属阳离子的存在使得过生物炭/LDHs更好地消除有毒重金属。Pb(II)、Cu(II)、Cr(VI)和 Cd(II)的最大吸附能力分别为 682.2、74.07、330.8 和35.59 mg/g。生物炭/LDH 复合材料去除重金属的机制包括各种过程，如静电吸引、离子交换、表面络合、同构取代和化学还原，这取决于目标重金属离子（阳离子或阴离子）的性质。对于二价阳离子，如Pb(II)、Cd(II)或Cu(II)，主要的去除机制包括与表面官能团的复合，以及离子交换、沉淀和同构取代。

Effective removal of heavy metals have also been widely reported using various biochar/LDH composites. High porosity and the presence of numerous functional groups and metal cations facilitates better elimination of toxic heavy metals by biochar/LDH compared to other modified biochars. As evident from Table 2, the maximum adsorption capacity of biochar/LDH was 682.2, 74.07, 330.8, and 35.59 mg/g for Pb(II), Cu(II), Cr(VI), and Cd(II), respectively. The removal mechanism of heavy metals by biochar/LDH composites involves a variety of processes such as electrostatic attraction, ion exchange, surface complexation, isomorphic substitution, and chemical reduction, depending on the nature of target heavy metal ions (cations or anions). In case of divalent cations such as Pb(II), Cd(II) or Cu(II), the primary removal mechanism involves complexation with surface functional groups along with other mechanisms including ion exchange, precipitation and isomorphic substitution.

（3）生物炭/LDH 复合材料去除抗生素的研究

Removal of Antibiotics by Biochar/LDH Composites

生物炭/LDH 复合材料也被用于从水中去除抗生素或其他药物，与原始生物炭相比，它们表现出更好的修复性能。生物炭/LDHs复合材料对四环素(TC)、双氯芬酸钠(DCF)、磺胺甲恶唑(SMX)的吸附能力分别为2114.43、1118.2、和26.21 mg/g。生物炭/LDHs复合材料对药物的去除亲和力增强是因为涉及了包括表面吸附、pi-pi相互作用和疏水相互作用、离子交换和氢键等多种机制。生物炭/MgAl 表面存在羟基（-OH）和烷氧基（-CO），与 TC 氨基（-氨基）和羟基（-OH）形成氢键。此外，pi-pi相互作用和生物炭/MgAl 与苯环的相互作用可以促进 TC 的吸附，TC吸附后，生物炭/MgAlFTIR 谱的 C 强度达到峰值。

Biochar/LDH composites have also been employed for the removal of antibiotics or other drugs from water, and they exhibited better remediation performance compared to pristine biochars. The adsorption capacity of biochar/LDH composites for tetracycline (TC), diclofenac sodium (DCF), carbon tetrachloride (CCl4), sulfamethoxazole (SMX), paracetamol and caffeine were reported to be 2114.43, 1118.2, 90.2, 2.25, 17.66 and 26.21 mg/g, respectively. The enhanced removal affinity of biochar/LDH composites towards drugs is attributed to the involvement of multi-mechanisms including surface adsorption, π-π and hydrophobic interactions, ion exchange and hydrogen bonding. The presence of hydroxyl (–OH) and alkoxy groups (–CO) on the surface of biochar/MgAl, form hydrogen bonding with the amino (–NH2) and hydroxyl groups (–OH) of TC. Besides, the reaction of Cdouble bondC groups on biochar/MgAl with benzene ring of TC via π-π interactions could aslo promote the TC adsorption. This was ascribed by a significant shift in OH, C–O and Cdouble bondC peaks intensities in the FTIR spectra of biochar/MgAl after TC adsorption.

（4）生物炭/LDH 复合材料在染料去除中的应用

Removal of Dyes by Biochar/LDH Composites

生物炭/LDH 复合材料具有良好的吸附性能，并具有良好的可回收性，如表 4 所示。吸附量最高的一种生物炭/LDH 上的水晶紫(CV)、二甲基蓝(MB)和钼、吖啶橙(AO)和孔雀石绿(MG)的量分别为354.05、406.67、412.08、108.6、470.96 mg/g。据报道，染料吸附到生物炭/LDH 复合材料上的机制与pi-pi相互作用、氢键、静电相互作用、阴离子交换、后充填和表面络合等多过程有关。

Biochar/LDH composites have demonstrated excellent adsorption characteristics with good recyclability for decolorization of dyes contaminated water, as depicted in Table 4. The highest adsorbed amount of crystal violet (CV), methylene blue (MB) and MO, acridine orange (AO) and malachite green (MG) onto biochar/LDH was 354.05, 406.67, 412.08, 108.6, 470.96 mg/g, respectively. Adsorption mechanism of dyes onto biochar/LDH composites was reportedly associated with multi-processes such as π-π interaction, hydrogen bonding, electrostatic interaction, anion exchange, pore-filling, and surface complexation.

 

 

（5）生物炭/LDH 复合材料在实际废水处理中的应用

Applications of Biochar/LDH Composites in Real Wastewater Treatment

生物炭/LDH 复合材料在真实水系统中去除各种污染物的去除性能很少被研究。然而，根据一些研究，可以得出结论，尽管在真实的水样中存在有机化合物和其他竞争离子，但生物炭/LDH 复合材料显示出可接受的重金属吸附作用。例如，生物炭/MgFe 复合物在24 小时内在实际废水中去除 97%的铅(II)，略低于超纯合成水中去除 99%的铅(II)。在实际污染的水环境中，生物炭磁性 LDO/碳（Mag-LDO(C) 和铜(II)比实验室的合成水样和水溶液具有更高的吸附亲和力。真实水系统中 Pb(II)和铜(II)与有机污染物的复合导致了生物炭/LDO 复合材料的高吸附。

The removal performance of various contaminants by biochar/LDH composites in real water systems is rarely investigated. However, based on a few studies, it could be concluded that despite the existence of organic compounds and other competitive ions in the real water sample, biochar/LDH composites showed acceptable sorption of heavy metals. For instance, biochar/MgFe composite exhibited 97% removal of Pb(II) within 24 h in real wastewater effluent which is slightly lower than 99% Pb(II) removal from ultrapure synthetic water (Yu et al., 2018). A recent study demonstrated, the potential of calcined MgAl/carbon composite for the elimination of heavy metals in various water systems. The biochar magnetic LDO/carbon (Mag-LDO/C) exhibited higher sorption affinity for Pb(II), and Cu(II) in a real polluted water environment, than that in the synthetic water samples and the aqueous solutions of the lab (Hou et al., 2020a). Complexation of Pb(II) and Cu(II) with organic contaminants in real water system contributed to higher sorption by biochar/LDO composites.

（6）挑战、机会和前景

Challenges, Opportunities, and Prospects

生物炭/LDH 复合材料已成为水净化的极好的可持续材料，但要充分利用这些材料的巨大特性进行实际应用，需要解决许多挑战。

Biochar/LDH composites have emerged as fabulous sustainable materials for water purification, yet numerous challenges that need to be addressed to fully exploit the tremendous characteristics of these materials for practical applications.

1. 生物炭/LDH 复合物在进行商业应用之前，必须仔细评估其潜在的环境毒性影响。

First, The potential environmental toxic effects of biochar/LDH composites must be carefully evaluated prior to their commercial applications.

2. 需要探讨生物炭/LDH 复合材料在二元尺度上具有成本效益、高效的吸附剂的可行性。

Second, the feasibility of biochar/LDH composites as cost-effective, efficient adsorbent on the indusial scale need to be explored.

3. 当前，生物炭/LDH 复合材料的常用 LDHs 是MgAl 和 MgFe 或NiAl。而研究CoFe、CoAl、NoFe、ZnAl、ZnFe、CuAl、CuAl 的有限。

Thrid, in literature, the commonly used LDHs to produce biochar/LDH composites are MgAl and MgFe or NiAl. There are limited studies that explored the applications of other LDHs such as CoFe, CoAl, NiFe, ZnAl, ZnFe, CuAl or CuFe for the synthesis of biochar/LDH composites.

4. 在生物炭/LDH 复合材料去除其他污染物，如酚、杀虫剂和核污染物的潜力等研究仍然较少。

Fourth, the potential of biochar/LDH composites for the removal of other pollutants like phenols, pesticides, and nuclear pollutants must also be explored.

5. 进一步探讨生物炭/LDH 复合材料在实际废水中的应用，以评估其在实际应用中的潜力。

Fifth, it is important to further explore the applications of biochar/LDH composites for real wastewater to assess their potential in practical applications.

结论与展望

Conclusion and Prospect

生物炭负载LDH 已经成为一种在合成低成本、可回收吸附材料的环保方法。生物炭/LDH 复合材料在从水中吸附重金属、染料、阴离子和药物方面表现出了巨大的潜力。虽然当前大规模生物炭/LDH 复合物的合成及其在实际废水系统中的应用较为少见。但是目前的研究进展表明，这种独特的材料在水净化方面有着光明的前景。

The hybridization of biochar with various LDHs has emerged as an eco-friendly approach for synthesizing low cost, sustainable and recyclable adsorbent materials in water purification. Biochar/LDH composites have exhibited tremendous potential for the adsorption of heavy metals, dyes, anions and pharmaceuticals from water. The significant challenges are large scale synthesis and applications of biochar/LDH composites in the real wastewater system. Although several challenges need to be tackled, the current research progress suggests that these distinctive materials have a bright future in water purification.

 

---

投稿者：高峰 博士研究生

审核导师：王宁 教授 |王慧 助理研究员