Highly catalytic activity of nickel nanoparticles generated in poly(methylmethacrylate)@poly(2-hydroxyethylmethacrylate) (PMMA@PHEMA) core–shell micelles for the reduction of 4-nitrophenol (4-NP)

Catalytic reduction of nitrophenols and dyes by HKUST-1/hydrogel composite

The effective removal of nitrophenols from wastewater is crucial due to their high carcinogenic risk. This research presents the development of a copper-based metal-organic framework (HKUST-1) integrated into a chitosan-graft-poly(acrylic acid) hydrogel. The hydrogel composite was evaluated as a catalyst for reducing nitrophenols and dyes using sodium borohydride (NaBH4) as a reducing agent. Various conditions were investigated for the reduction of 4-nitrophenol (4-NP) to the less harmful 4-aminophenol (4-AP), including catalyst dosage, NaBH4 concentration, initial 4-NP concentration, temperature, and pH. The catalyst was able to completely reduce 4-NP within 25 minutes at a dosage of 3 g L-1 and a NaBH4 concentration of 300 mM. The reduction rate increased with higher temperatures, with an Arrhenius activation energy of 54.4 kJ mol-1. Common anions found in surface water, such as Cl-, NO3 -, SO4 2-, and HCO3 -, had a slight impact on the reduction rate of 4-NP. When tested in real water environments, the reduction rate decreased, but complete conversion was still achieved. Additionally, the composite successfully reduced 100% of 2-nitrophenol, 100% of methyl orange, and 69% of Congo red. Overall, the hydrogel composite has shown significant potential as a catalyst for reducing various organic pollutants with high efficiency and easy separation through filtration.

Chitosan-grafted hydrogels for heavy metal ion adsorption and catalytic reduction of nitroaromatic pollutants and dyes

Chitosan-grafted-poly(acrylic acid) (CS-g-PAA) and chitosan-grafted- poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (CS-g-P(AA-co-AMPS)) hydrogels were synthesized and then employed as adsorbents for the effective removal of Cu2+ and other heavy metal ions. The effect of hydrogel's composition on the Cu2+ adsorption was explored. The CS-g-PAA hydrogel demonstrated a superior adsorption capacity compared to pristine CS, PAA hydrogel, and CS-g-P(AA-co-AMPS) hydrogels. The adsorption followed the Langmuir isotherm model, and the pseudo-second order kinetic model. Additionally, the CS-g-PAA hydrogel exhibited relatively high adsorption performances toward Cr3+, Co2+, Ni2+, Pb2+, and Zn2+. Metal ions adsorbed within CS-g-PAA hydrogels underwent reduction to their corresponding metallic states and were reutilized as catalysts for the reduction of 4-nitrophenol. The comparative catalytic performances of the metal species in the hydrogel were in the order of Cu > Ni > Co > Zn. The reduction efficiency of Cu-CS-g-PAA increased with increased catalyst dosage, NaBH4 concentration, and temperature. A very low activation energy of 3.7 kJ/mol was observed. The catalyst maintained high catalytic performance even when subjected to real water samples and proved its reusability for up to three cycles. Moreover, the catalyst could effectively reduce 2-nitrophenol and methyl orange.