Selective Adsorption toward Hg(II) and Inhibitory Effect on Bacterial Growth Occurring on Thiosemicarbazide-Functionalized Chitosan Microsphere Surface

Abstract

The work presented here aims to fabricate dual-purpose adsorbent with adsorption selectivity for Hg(II) and antibacterial activity. TSC-PGMA-MACS microspheres were first constructed via esterification of malic acid (MA) with chitosan (CS) and through successively grafting glycidyl methacrylate (GMA) and thiosemicarbazide (TSC) onto MACS microsphere surfaces. Fourier transform infrared spectroscopy, elemental analysis, energy-dispersive X-ray spectrometry, X-ray diffraction, differential scanning calorimetry, thermogravimetry, differential thermogravimetry, scanning electron microscopy, and Brunauer-Emmett-Teller results provided ample evidence that new mesoporous adsorbent, with 35.340 m2 g-1 of specific surface area and abundant -NH2 and C═S, was successfully fabricated and had loose crystalline, thermodynamically stable, and well-defined architectures, beneficial for Hg(II) adsorption and bacterial cell killing. Optimal adsorption parameters were determined via varying pH, time, concentrations, and temperatures, and pH 6.0 was chosen as an optimal pH for Hg(II) adsorption. Adsorption behavior, described well by pseudo-second-order kinetic and Langmuir isotherm models, and thermodynamic parameters implied a chemical, monolayer, endothermic, and spontaneous adsorption process, and the maximum adsorption capacity for Hg(II) was 242.7 mg g-1, higher than most of the available adsorbents. Competitive adsorption exhibited excellent adsorption selectivity for Hg(II) in binary-metal solutions. Besides, TSC-PGMA-MACS microspheres had outstanding reusability even after five times recycling, with adsorption capability loss <14%. Several potential adsorption sites and bonding modes were proposed. Notably, TSC-PGMA-MACS microspheres before and after adsorption were of high antibacterial activity against Escherichia coli and Staphylococcus aureus (MICs, 2 and 0.25 mg mL-1), superior to CS powders, and possible antibacterial mechanisms were also summarized. Altogether, dual-purpose TSC-PGMA-MACS microspheres might be promising adsorbent for contaminated water scavenging.