Microwave-assisted one-pot preparation of magnetic cactus-derived hydrochar for efficient removal of lead(Ⅱ) and phenol from water: Performance and mechanism exploration

In-situ anchoring of ZIF-8 nanoparticles on sodium alginate aerogel for efficient and rapid phenol adsorption from wastewater

The deep purification of highly toxic phenol in wastewater is a water purification issue of concern. Metal-organic frameworks (MOFs) have been widely used in the field of adsorption and separation owing to their advantages of high porosity and abundant active sites. However, powdered MOFs are easy to agglomerate and difficult to separate, which poses a great challenge to their adsorption performance and recycling, severely limiting their practical applications. To overcome these difficulties, an in situ nucleation and growth of ZIF-8 nanoparticles on sodium alginate aerogel was proposed to achieve efficient phenol adsorption. The introduction of ZIF-8 increases the number of adsorption sites. 3D aerogel structure effectively prevents ZIF-8 from agglomerating and increases the specific surface area to facilitate the exposure of active sites. This composite structure balances the utility and the powder nature of ZIF-8. Benefiting from the synergistic effect of advantageous structure, ZIF-8@SA-AG exhibits high adsorption capacity (91.5 mg g-1) within 60 min at an initial concentration of 70 mg L-1, which outperforms most of the reported phenol adsorbents under the similar conditions. This study provides a feasible solution for custom processing of MOFs powder and construction of diversified composite macro bulk adsorbents.

Mechanism and application of sulfhydryl-modified chitosan derivative for decontamination of Pb(II) and Cd(II) in water bodies

The accumulation of lead and cadmium in water bodies is a serious threat to environmental safety and human health, and they must be removed from wastewater. Based on this this study, a novel sulfhydryl-modified chitosan derivative (SHCS) was prepared by grafting method using chitosan as a substrate for the removal of Pb(II) and Cd(II) from polluted water bodies. The results showed that the SHCS derivative was a mesoporous biosorbent with a specific surface area of 0.0505 cm3/g. The adsorption kinetics of the adsorbent on the pollutants conformed to the pseudo-first-order and pseudo-second-order models (R2 > 0.99). The adsorption isotherms all followed the Langmuir model (Pb(II): R2 = 0.9388, Cd(II): R2 = 0.9592). The maximum adsorption capacities of SHCS were 209.27 mg/g and 64.19 mg/g for Pb(II) and Cd(II), respectively. The free energy of adsorption ΔGθ < 0 indicates that the adsorption process is a spontaneous reaction, in which the adsorption of lead is an adsorptive process (ΔHθ > 0) and the adsorption of cadmium is an exothermic process (ΔHθ < 0). The addition of NaNO3 and cations (K+, Ca2+, and Mg2+) did not affect the adsorption process of Pb(II) and Cd(II). The surface complexation and electrostatic attraction mechanisms controlled the decontamination of Pb(II) and Cd(II) by SHCS in water. Most importantly, the SHCS derivative was effective in removing low concentrations of Pb(II) and Cd(II) from three real wastewater samples as well as a simulated electroplating wastewater.

Effect of oxygen-containing functional group contents on sorption of lead ions by acrylate-functionalized hydrochar

The surface functional groups of hydrochar are crucial to its surface properties, and their contents are strongly positively correlated with the adsorption performance. In this study, acrylate-functionalized hydrochar (AHC) with varying contents of O-containing functional groups (OFGs) was synthesized via hydrothermal carbonization (HTC) of bamboo, acrylic acid and an initiator, and then deprotonated with NaOH. The AHCs were analyzed by various characterization techniques. During HTC, the higher amount of acrylic acid added led to higher carbon, oxygen and carboxyl contents, and to the larger specific surface area and pore volume of AHC. The adsorption kinetics, isotherms, thermodynamic, ionic strength and pH effects of Pb(II) on AHC were studied. Adsorption isotherms and kinetics obeyed Langmuir and pseudo-second-order models, respectively, indicating adsorption is monolayer chemical process. The adsorptive ability was well linearly related to the OFG contents of AHC. When acrylic acid was added to 25 mL during HTC, the adsorbing ability of AHC over Pb(II) reached 193.90 mg g-1. Hence, direct HTC of acrylic acid, biomass and an initiator can prepare hydrochar with controllable OFG contents, which is a prospective adsorbent for treating metal cations.