CIQTEK SEM and EPR Reveal a New Pathway for Nickel-Citrate Removal
With the rapid expansion of new energy, mining, metallurgy, and electroplating industries, nickel pollution in water bodies has become a growing threat to environmental quality and human health. During industrial processes, nickel ions often interact with various chemical additives to form highly stable heavy-metal organic complexes (HMCs). In nickel electroplating, for example, citrate (Cit) is widely used to improve coating uniformity and brightness, but the two carboxyl groups in Cit readily coordinate with Ni²⁺ to form Ni–Citrate (Ni-Cit) complexes (logβ = 6.86). These complexes significantly alter nickel’s charge, steric configuration, mobility, and ecological risks, while their stability makes them challenging to remove with conventional precipitation or adsorption methods. Currently, "complex dissociation" is regarded as the key step in removing HMCs. However, typical oxidation or chemical treatments suffer from high cost and complicated operation. Therefore, multifunctional materials with both oxidative and adsorptive capabilities offer a promising alternative. Researchers from Beihang University, led by Prof. Xiaomin Li and Prof. Wenhong Fan, used the CIQTEK scanning electron microscope (SEM) and electron paramagnetic resonance (EPR) spectrometer to conduct an in-depth investigation. They developed a new strategy using KOH-modified Arundo donax L. biochar to efficiently remove Ni-Cit from water. The modified biochar not only showed high removal efficiency but also enabled nickel recovery on the biochar surface. The study, titled “Removal of Nickel-Citrate by KOH-Modified Arundo donax L. Biochar: Critical Role of Persistent Free Radicals”, was recently published in Water Research. Material Characterization Biochar was produced from Arundo donax leaves and impregnated with KOH at different mass ratios. SEM imaging (Fig. 1) revealed: The original biochar (BC) exhibited a disordered rod-like morphology. At a 1:1 KOH-to-biomass ratio (1KBC), an ordered honeycomb-like porous structure was formed. At ratios of 0.5:1 or 1.5:1, pores were underdeveloped or collapsed. BET analysis confirmed the highest surface area for 1KBC (574.2 m²/g), far exceeding other samples. SEM and BET characterization provided clear evidence that KOH modification dramatically enhances porosity and surface area—key factors for adsorption and redox reactivity. Figure 1. Preparation and characterization of KOH-modified biochar. Performance in Ni-Cit Removal Figure 2. (a) Removal efficiency of total Ni by different biochars; (b) TOC variation during Ni–Cit treatment; (c) Effect of Ni–Cit concentration on the removal efficiency of 1KBC; (d) Effect of pH on the removal performance of 1KBC; (e) Influence of coexisting ions on Ni–Cit removal by 1KBC; (f) Continuous-flow removal performance of Ni–Cit by 1KBC. (Ni–Cit = 50 mg/L, biochar dosage = 1 g/L) Batch experiments de...