High reusability and adsorption capacity of acid washed calcium alginate/chitosan composite hydrogel spheres in the removal of norfloxacin.

Calcium alginate (CA) hydrogel spheres were widely used as adsorbents to remove organics, but their adsorption capacities and reusability to some antibiotics are unsatisfactory. In this study, calcium alginate/chitosan (CA/CTS) hydrogel spheres were prepared as precursors. Acid-washed CA/CTS (CA/CTS-M) hydrogel spheres (310.6 mg/g) behaved much better adsorption capacity of norfloxacin (NOR) than CA (69.5 mg/g) and CA/CTS (87.7 mg/g) hydrogel spheres. Astonishingly, after being reused for 15 cycles, CA/CTS-M has no loss of NOR adsorption capacity. In the original idea, acid wash was expected to remove the chitosan in CA/CTS hydrogel spheres for obtaining a larger specific surface area. Both scanning electron microscopy and Brunauer-Emmett-Teller test showed that acid wash can remove CTS from CA/CTS hydrogel spheres to increase the specific surface area. However, part of the chitosan remained in CA/CTS-M, having a role to enhance the structural stability of the material, because the acid-washed CA (about 2 mm) has a significantly smaller diameter than CA/CTS-M (about 3 mm). According to the influence of pH and density functional theory calculations, electrostatic attraction is the key driving force of NOR adsorption. Importantly, acid wash led to more negative-charged surface characterized by Zeta potential, which is the main reason of the significantly enhanced adsorption capacity of CA/CTS-M in removal of NOR. In short, CA/CTS-M hydrogel spheres are environment friendly and highly stable adsorbents with high adsorption capacity in the removal of NOR.

Nitrogen-doped carbon materials prepared using different organic precursors as catalysts of peroxymonosulfate to degrade sulfamethoxazole: First-time performance leading to the incorrect selection of the best catalyst.

Nitrogen-doped carbon materials are effective catalysts for peroxymonosulfate (PMS) activation to eliminate organic contaminants. In this research, the activity of nitrogen-doped carbon materials was significantly improved by optimizing the carbon source, and the reusability of the catalyst is used to select the best catalyst instead of depending on the performance in the first use, for avoiding the "short-life" catalyst with great initial activity. Fixing ferric nitrate nonahydrate and melamine as the metal and nitrogen sources, four catalysts were prepared using glucose, glucosamine hydrochloride, dopamine, and trimesic acid as the carbon sources, respectively. Based on the performance in PMS activation for sulfamethoxazole (SMX) removal, in the first use, the activity was Fe-DA-CN (carbon source: dopamine) > Fe-BTC-CN (carbon source: trimesic acid) > Fe-GLU-CN (carbon source: glucosamine) > Fe-DGLU-CN (carbon source: glucose). With no washing for the second time use, the activity was Fe-BTC-CN (0.135 min-1) â‰« Fe-DA-CN (0.037 min-1) > Fe-GLU-CN (0.032 min-1) > Fe-DGLU-CN (0.017 min-1). The large specific surface area, superior graphitization, and high CO/C-N group content endow Fe-BTC-CN with high ability in PMS activity. Surface-bound radicals are responsible for SMX elimination, and most of the SMX degradation intermediates have lower ecotoxicity than SMX.

Simply synthesized sodium alginate/zirconium hydrogel as adsorbent for phosphate adsorption from aqueous solution: Performance and mechanisms.

The traditional zirconium hydrogel beads were synthesized by multi-step method, which was comparatively complex. In this study, a high phosphate removal efficient sodium alginate/zirconium (SA/Zr) hydrogel was synthesized by a simple method, with the phosphate adsorption performance and mechanism be explored. The results showed that the adsorption capacity of SA/Zr hydrogel to phosphate was greatly affected by pH. With the increase of initial pH (3-11), the adsorption capacity of SA/Zr for phosphate descended. The phosphate adsorption capacity of SA/Zr hydrogel exceeded 120 mg PO43-/g at pH 2-7, while reaching the maximum adsorption capacity at pH 3 (256.79 mg PO43-/g). The process of adsorption kinetics was well fitted by intraparticle diffusion model, indicating that there was chemical adsorption during the adsorption process. The Redlich-Peterson isotherm model can well accord with isotherm data. In addition, the material showed high selectivity to phosphate. Besides, combining X-ray photoelectron spectroscopy with Zeta potential results suggested that when the pH value was less than 4.19, SA/Zr hydrogel adsorbed phosphate by electrostatic attraction and hydrogen bonding while the adsorption was made mainly through ligand exchange when pH value was higher than 4.19.