Estimating the Shear Resistance of Flocculated Kaolin Aggregates: Effect of Flocculation Time, Flocculant Dose, and Water Quality

Straw-Derived Activated Carbon Decorated with Ag3PO4 for Organic Pollutant Removal by a Circular Degradation Mechanism: Adsorption and Photocatalysis

The escalating problem of water pollution has become an urgent concern, as it significantly undermines people's quality of life and overall public health. The increasing severity of water pollution represents a global challenge, with profound implications for human society. In this study, hydrothermal carbonization coupled with alkaline activation was utilized to repurpose barley straw into activated carbon (AC) as an absorbent. Silver phosphate (Ag3PO4) was synthesized as a potent photocatalyst. Subsequent ultrasound-assisted loading integrated the robust adsorptive capabilities of the AC with the advanced photocatalytic efficiency of silver phosphate, resulting in a superior composite material (AC/Ag3PO4) and implementing a novel "absorption-photocatalysis" active circular degradation strategy to remove hazardous organics in water. Comprehensive characterization assays confirmed the successful synthesis and incorporation of Ag3PO4 onto the AC scaffold. The composite with a Ag3PO4 concentration of 3 wt % exhibited a high methylene blue (MB) removal efficiency of 99.4% within 100 min. The reaction rate of this composite surpassed that of standalone AC by a factor of 2.89. Furthermore, cyclic regeneration studies via adsorption-desorption methodologies revealed the composite's resilience and sustained performance. The MB removal efficiency was maintained at 85.5% over five consecutive cycles, demonstrating the composite's remarkable stability. The integration of adsorptive and photocatalytic functionalities within a single system mitigates potential secondary pollution arising during the AC's desorption phase and enhances the organic contaminant removal efficiency. Moreover, the utilization of this integrated material reduces the quantity of chemicals and energy required for conventional adsorption water treatment techniques, as the material harnesses sunlight or alternative light sources to catalyze contaminant decomposition. This reduces the dependence on chemical treatment agents, contributing to resource conservation and alleviating environmental burdens. This pioneering approach offers a novel paradigm for addressing pollutant challenges in aqueous environments.

Atomic Force Microscopy and Molecular Dynamic Simulation of Adsorption of Polyacrylamide with Different Chemistries onto Calcium Carbonate

This study investigates the interaction of polyacrylamide (PAM) of different functional groups (sulfonate vs. carboxylate) and charge density (30% hydrolysed vs. 10% hydrolysed) with calcium carbonate (CaCO3) via atomic force microscopy (AFM) and partly via molecular dynamic (MD) simulations. The PAM used were F3330 (30% hydrolysed), AN125 (25% sulfonated), and AN910 (% hydrolysed). A total of 100 ppm of PAMs was prepared in 0.1% NaCl, 3% NaCl, and 4.36% NaNO3 to be employed in AFM experiments, while oligomeric models (30 repeating units) of hydrolysed polyacrylamide (HPAM), sulfonated polyacrylamide (SPAM), and neutral PAM (NPAM) were studied on a model calcite surface on MD simulations. AFM analysis indicated that F3330 has a higher average adhesion and interaction energy with CaCO3 than AN125 due to the bulky sulfonate side group of AN125 interfering with SPAM adsorption. Steric repulsion of both PAMs was similar due to their comparable molecular weights and densities of the charged group. In contrast, AN910 showed lower average adhesion and interaction energy, along with slightly longer steric repulsion with calcite than F3330, suggesting AN910 adopts more loops and tails than the slightly flatter F3330 configuration. An increase in salt concentration from 0.1% to 3% NaCl saw a reduction in adhesion and interaction energy for F3330 and AN125 due to charge screening, while AN910 saw an increase, and these values increased further at 4.36% NaNO3. MD simulations revealed that the salt ions in the system formed salt bridges between PAM and calcite, indicating that the adhesion and interaction energy observed from AFM are likely to be the net balance between PAM charged group screening and salt bridging by the salt ions present. Salt ions with larger bare radii and smaller hydrated radii were shown to form stronger salt bridges.

Research Progress of the Ion Activity Coefficient of Polyelectrolytes: A Review

Polyelectrolyte has wide applications in biomedicine, agriculture and soft robotics. However, it is among one of the least understood physical systems because of the complex interplay of electrostatics and polymer nature. In this review, a comprehensive description is presented on experimental and theoretical studies of the activity coefficient, one of the most important thermodynamic properties of polyelectrolyte. Experimental methods to measure the activity coefficient were introduced, including direct potentiometric measurement and indirect methods such as isopiestic measurement and solubility measurement. Next, progress on the various theoretical approaches was presented, ranging from analytical, empirical and simulation methods. Finally, challenges for future development are proposed on this field.

Special Issue: Synthesis, Processing, Structure and Properties of Polymer Materials

Polymeric materials are widely used in many different technical fields [...].