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生物炭是生物质在限氧条件下制备的一类含碳固体物质,因其在土壤改良、污染物固定、提高农产品产质量等方面的广泛应用而备受研究者关注[1-4]。但生物炭对污染物的吸附容量受其特性的限制(如表面官能团含量、孔隙结构及比表面积、pH值、阳离子交换量、Zeta电位等),此外传统生物炭还存在诸多不足,如对污染物的吸附容量较低、含有少量污染物(重金属)、施用后难以从环境中分离等,这些因素限制了生物炭的推广和应用。值得注意的是,生物炭改性可有效改变其对污染物的吸附及降解。如硝酸改性可以增加生物炭羧基和负电荷含量,使其对U(Ⅵ)的吸附量提高40倍[5];重金属改性生物炭能够增加生物炭中持久性自由基的浓度和类型,增强过硫酸盐自由基对多氯联苯的降解[6];而硫铁改性生物炭能有效降低污染稻田土中Cd的生物可利用性,减少Cd在不同水稻组织中的积累,同时增加水稻总叶绿素含量以及根、茎和籽粒生物量[7]。然而有研究报道了HF和HCl改性会减少对Cd的吸附;过渡金属改性生物炭后其持久性自由基浓度的减少抑制了有机物的降解;与此同时还有研究表明不同化学剂量的KOH改性可能导致生物炭性质出现极大差别[8]。因此不同方法改性对生物炭性质有何影响?性质改变后对污染物的吸附与降解是促进还是抑制?促进或抑制的机制如何?这些问题需亟待解决。
本文在阐述改性方法对生物炭性质影响的基础之上,综述了生物炭改性对其吸附与降解污染物的影响机制,并提出改性生物炭需进一步研究的相关科学问题。这将为科学改性生物炭提供选择依据,有助于全面理解改性生物炭的环境效应及促进生物炭的应用推广。
生物炭改性及其对污染物吸附与降解行为的研究进展
Research progress on modification of biochar and its adsorption and degradation behavior
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摘要: 生物炭因其原料来源广泛、含碳量丰富、成本低等特点被广泛应用于污染环境修复领域。生物炭能否高效去除污染物的关键点在于生物炭所具备的理化性质。生物炭改性能促使生物炭理化性质改变(如比表面积增加、灰分含量降低、丰富表面官能团等),从而促进或抑制其对污染物吸附与降解行为。然而改性生物炭对污染物的吸附或降解行为受改性条件(物理、化学及生物等)和污染物性质的影响。文章回顾了国内外关于生物炭改性方法,以及生物炭改性对污染物吸附与降解行为研究的主要进展。在此基础上,总结了生物炭改性方法、改性机理以及对污染物吸附与降解行为的影响机制,并进一步提出了未来的研究重点和尚待解决的相关科学问题。Abstract: Biochar has been widely applied in the field of environmental remediation due to its various feedstock, rich carbon content and low cost. The physical and chemical properties of biochar are key to efficient removal of pollutants. Modification of biochar can change its physicochemical properties (e.g., specific surface area, ash content, and surface functional groups, etc.), thus promoting or inhibiting adsorption and degradation of pollutants on biochar. Normally, modification conditions (physical, chemical and biological treatment) and property of pollutants determine the adsorption or degradation behavior of biochar. This paper reviewed current methods of biochar modification and research progress on adsorption and degradation of pollutants on modified biochars. Based on this, methods and mechanisms of biochar modification, as well as influence on the adsorption and degradation of pollutants, were summarized. At the end of the paper, future research focuses and possible difficulties were prospected.
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Key words:
- biochar /
- modified /
- heavy metal /
- organic pollutants /
- adsorption /
- degradation
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表 1 物理改性生物炭特性变化研究
Table 1. Research on the biochar properties of physical modification
表 2 酸改性生物炭特性变化研究
Table 2. Research on the biochar properties of acid modification
生物质
Biomass热解温度/℃
Pyrolysis temperature改性试剂
Modification reagents理化特性
Properties参考文献
Reference椰子壳 300、500、700 HNO3 灰分含量减少,CEC增加,酸性官能团增加,比表面积增大 [17] 植物园杂木 700 H2SO4 孔隙结构更发达,热稳定性降低,—SO3H、—OH、—COOH等官能团增加 [19] 柳木 700 HCl 矿物成分减少,微孔增加 [25] 松木 200—650 H3PO4 总孔体积和比表面积增加,C含量增加,生物炭产率提高,改性使生物炭
保留了更多的极性官能团[22] 稻草 120 柠檬酸 促进孔结构发展,比表面积减小,可提取硅含量降低,—OH、脂肪族基团
(—CH3、—CH2)增加[23] 桉树 — 洒石酸 —COOH增加,(N + O)/C增加,比表面积减小 [21] 乙酸 —COOH增加,(N + O)/C增加,比表面积减小 表 3 碱改性生物炭特性变化研究
Table 3. Research on the biochar properties of alkali-modification
表 4 有机试剂改性生物炭特性变化研究
Table 4. Research on the biochar properties of organic reagent modification
表 5 金属氧化物或金属盐类改性生物炭特性变化研究
Table 5. Research on the biochar properties of metal oxides or metal salts modification
生物质
Biomass热解温度/℃
Pyrolysis
temperature改性试剂
Modification
reagents理化特性
Properties参考文献
Reference油菜秸秆 600 KMnO4 比表面积和孔隙体积增大,平均孔径减小 [41] 杨木 300、600、900 FeSO4 Fe、S含量增加,比表面积增加,S在生物炭表面分散性较好 [39] FeCl3 Fe、Cl含量增加,比表面积增加,Cl堆积在生物炭表面 玉米芯 500 TiO2 TiO2分散在生物炭表面,光解反应中·OH增加 [48] 大豆秸秆 500 MgCl2 Mg含量和O含量增加,C含量减少,比表面增大,孔隙结构增大,表面粗糙多孔 [49] AlCl3 Al含量和O含量增加,C含量减少,比表面增大,孔隙结构增大,表面粗糙多孔 污泥 700 ZnCl2 比表面积增加,结晶度增加 [50] 表 6 纳米材料改性生物炭特性变化研究
Table 6. Research on the biochar properties of nanomaterials modification
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