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三嗪类除草剂被广泛应用于农田、公园、高尔夫球场及住宅草坪等环境中阔叶杂草的控制,具有除草效率高、价格低廉等突出优点,其中代表性的品种有莠去津、西玛津、西草通和西草净等[1]. 三嗪类除草剂稳定性高,不易被生物降解,此外,水溶性大且半衰期长等特点使其极易残留于水土环境中,进而对非靶标生物和人体健康造成威胁[2 − 4]. 因此,亟需探索建立环保、高效的三嗪类除草剂降解方法,以减轻其可能对环境产生的不良影响.
近年来,以聚合氮化碳纳米材料为基础的光催化降解技术,被用于多种环境污染物的降解去除[5 − 8]. 聚合氮化碳是一种新型半导体催化剂,具有合成简便、物理化学稳定性好、可见光响应等突出优点[9]. 然而聚合氮化碳的应用仍受到光致空穴-电子重组率高和比表面积小两个突出问题的限制,金属掺杂是提高聚合氮化碳催化性能的有效途径之一[10]. 通过超声或热剥离等方式也可提高聚合氮化碳的比表面积[11].
金属铁含量丰富,价格低廉,与铂、银和铜等金属相比具有更突出的环境友好性[12]. 浒苔(Enteromorpha prolifera)属石莼科大型绿藻,近年来在我国黄海及东海海域爆发增殖,引发绿潮现象. 浒苔本身无毒,但大量繁殖会极大程度地消耗海水中的氧气,对其他水生生物造成不良影响,后续打捞处理也会使成本大幅增加[13 − 14]. 浒苔含铁量高达0.2%wt—0.5%wt, 在“中国食物营养成分表”中排名第一,若将其与聚合氮化碳结合,可以实现铁掺杂和废弃生物质再利用的双重目标.
本研究采用超声辅助-高温聚合法制备了浒苔生物炭/氮化碳复合材料(BCE/CN),并研究了复合材料对西玛津等4种代表性三嗪类除草剂的光催化降解效率. 利用X射线光电子能谱(XPS)、高角环形暗场-扫描透射电子显微镜(HAADF-STEM)等表征手段,明确复合材料中Fe的形态及键合形式,系统研究复合催化材料用量、除草剂初始浓度、反应温度和pH值对三嗪除草剂降解效率的影响,并结合活性物种捕获实验,对降解机制进行深入阐释. 为三嗪类除草剂环境污染治理和废弃生物质再利用提供了理论和技术支撑.
浒苔生物炭/氮化碳复合材料对三嗪类除草剂的可见光催化降解性能与机制
Degradation performance and mechanism of Enteromorpha prolifera biochar/carbon nitride composites on triazine herbicides
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摘要: 针对聚合氮化碳(CN)材料比表面积小,光致电子-空穴重组率高的问题,本研究利用废弃浒苔,结合原位煅烧法,制备了浒苔生物炭/氮化碳复合材料(BCE/CN),用于三嗪类除草剂的催化降解. 浒苔中富含的铁元素可有效提高CN对可见光的吸收利用性能,BCE/CN对西玛津、莠去津、西草净和莠灭净4种三嗪除草剂的1 h降解率分别提升43.0%、22.5%、31.0%和66.7%. 高角环形暗场-扫描透射电子显微镜结果表明,Fe在复合材料中以单原子和团簇形式分布,并与CN中的N以配位键形式结合. 活性物种捕获实验证明,光致空穴在除草剂降解过程中发挥决定性作用,单线态氧以及羟基自由基也一定程度参与反应. 此外,系统研究了催化剂用量、除草剂初始浓度、反应温度和pH值对降解过程的影响,并在实际环境水样中评价BCE/CN的催化活性. 本研究为三嗪类除草剂的高效降解提供了新方法,也为废弃生物质再利用提供了新思路.Abstract: In order to solve the problems of low specific surface area and high electron-hole recombination rate of polymeric carbon nitride (CN) material, the biochar/carbon nitride composite (BCE/CN) was prepared by in-situ calcination of waste Enteromorpha prolifera and applied for catalytic degradation of triazine herbicides. Iron present in Enteromorpha prolifera effectively enhances CN’s absorption and utilization of visible light. The simultaneous degradation efficiencies of BCE/CN for simazine, atrazine, simetryne and ametryn improved 43.0%, 22.5%, 31.0% and 66.7%, respectively, within one hour. High angle annular dark field scanning TEM verified the presence of Fe single atom and nanocluster in BCE/CN catalyst, which were coordinated with N of CN substrate. Results of quenching experiments emphasized the prominent role of h+, and the joint contribution from 1O2 and ·OH during degradation process. In addition, the effects of catalyst dosage, initial concentration of herbicide, reaction temperature and pH value on the degradation process were systematically studied, and the catalytic activity of BCE/CN was evaluated in actual environmental water matrices. This study provides a new method for the efficient degradation of triazine herbicides, and a new perspective for the reuse of waste biomass.
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Key words:
- carbon nitride /
- herbicide /
- photocatalytic degradation /
- mechanism /
- Enteromorpha prolifera.
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表 1 4种目标除草剂的分子结构及质谱信息
Table 1. Molecular structure and MS/MS parameters of four investigated herbicides
除草剂
Herbicide结构
Structure母离子
Precursor ions子离子
Product ions去簇电压/V
DP碰撞电压/V
CE西玛津
Simazine202.1 132.0*
103.985
7025
34莠去津
Atrazine216.0 174.1*
104.070
7024
40西草净
Simetryn214.1 124.2*
96.073
6026
31莠灭净
Ametryn228.0 186.0*
95.973
9026
33*定性离子对 Quantitative ion pair. 表 2 催化剂材料的比表面积,孔体积和平均孔径
Table 2. The SBET, pore volume and average pore diameter of the prepared samples
材料
Sample比表面积/(m2·g−1)
SBET孔体积/(m3·g−1)
Pore volumes平均孔径/nm
Average pore diametersCN 85.26 0.37 15.59 BCE 5.39 0.022 16.74 BCE/CN 109.29 0.39 17.03 -
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