Chemically-Activated Biochar from Ricinus communis L. Cake and Their Potential Applications for the Voltammetric Assessment of Some Relevant Environmental Pollutants

Biochar is a rich-carbon material highly functionalized, which allows the use as electrodes modifier for preconcentration and voltammetric determination of several species. This work describes a castor cake biochar production and chemical activation with different reaction conditions using HNO3 and/or H2O2. Biochar samples were characterized using scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman and zeta potential. Carbon paste modified electrodes (CPME) have been constructed using different biochar samples to evaluate the adsorptive capacity for the spontaneous preconcentration and voltammetric determination of Pb2+, Cd2+, Cu2+ and Ni2+ ions, paraquat and methyl parathion pesticides. The activation treatments promoted modifications in the elemental, morphological and structural biochar characteristics. Activated biochar CPMEs showed increase in the current signal around 15 and 2.5 times higher than unmodified and precursor biochar electrode, respectively. N2 sample (HNO3, 60 °C for 3.0 h) presented the better response signals for all compounds. This was attributed to the more effective surface oxidation, promoting a high porosity, acid character and amount of acid functional groups. Besides that, this greater analytical response allows the CPME-N2 application as a passive sampler for the voltammetric determination of inorganic and organic contaminants for environmental management in aqueous matrices.

生物炭（Biochar）是一种富含碳的高功能化材料，可用作电极修饰剂，用于多种分析物的预富集与伏安法测定。本研究报道了以蓖麻饼为原料制备生物炭的工艺，并采用硝酸（HNO3）和/或过氧化氢（H2O2）在不同反应条件下对其实施化学活化。采用扫描电子显微镜（Scanning Electron Microscopy, SEM）、能量色散光谱（Energy Dispersive Spectroscopy, EDS）、热重分析（Thermogravimetric Analysis, TGA）、傅里叶变换红外光谱（Fourier-Transform Infrared Spectroscopy, FTIR）、拉曼光谱（Raman Spectroscopy）及zeta电位法对所得生物炭样品进行了系统表征。采用不同生物炭样品制备了碳糊修饰电极（Carbon Paste Modified Electrode, CPME），以评估其对Pb²+、Cd²+、Cu²+、Ni²+四种重金属离子，以及百草枯和甲基对硫磷两种农药的自发预富集吸附能力与伏安法测定性能。活化处理可显著改变生物炭的元素组成、形貌与结构特性。经活化的生物炭碳糊修饰电极的电流信号分别较未修饰电极与原始生物炭电极提升约15倍与2.5倍。其中，N2样品（采用HNO3在60℃下反应3.0小时）对所有目标分析物均表现出最优的响应信号。该优异性能源于更充分的表面氧化作用，可赋予材料高孔隙度、酸性表面特质与丰富的酸性官能团。此外，该电极优异的分析响应性能使其可作为被动采样器，用于水基质中无机与有机污染物的伏安法测定，为水环境环境管理提供技术支撑。