Adsorption of Anionic Polyacrylamide onto Coal and Kaolinite Calculated from the Extended DLVO Theory Using the van Oss-Chaudhury-Good Theory

Experimental and simulation studies on the improvement of coal dust pollution by an aqueous solution of sodium α-alkenylsulfonate and amino acid-based surfactants

The use of surfactants is crucial for the prevention and control of coal dust pollution in coal mining operation areas, yet there still exist many challenges in the control of coal dust pollution. In this paper, the green biomass-based amino acid surfactant sodium myristoyl glutamate (SMG) and the anionic surfactant sodium α-alkenyl sulfonate (AOS) were selected to investigate the improvement of coal dust wettability by single and binary solutions from the macroscopic and microscopic perspectives. Molecular simulations were used to reveal the microscopic mechanism of the wettability of coal dust by the different solutions. Experimental measurements showed that the contact angle of the AOS + SMG aqueous solution was as low as 13.8° on a coal surface. Coating the coal dust with the AOS + SMG solution reduced the surface tension by 12.02% compared to coating the coal with a single component solution. Additionally, the use of the binary AOS + SMG solution increased the hydrophilic group content in the coating by 11.77% compared to a single component solution, and the linkage between hydrophilic groups was enhanced, which pulls the water molecules to wet the coal dust. These research results should provide a new way to promote more environmentally friendly coal dust pollution control technology.

Molecular dynamics simulations of the solubility and conformation change of chitosan grafted polyacrylamide: Impact of grafting rate

Graft modification is an effective approach to improve the water solubility and molecular weight of chitosan. This work investigated the effect of grafting rate on water solubility of chitosan-grafted polyacrylamide (Chi-g-PAM) using molecular dynamics simulations. The intramolecular and intermolecular interaction between Chi-g-PAM with the grafting rate of 100%-250% and water together with the conformation change were analyzed by radial distribution function (RDF), radius of gyration, solvation free energy (ΔGSFE), mean square displacement, diffusion coefficient and shear viscosity. The results showed that the intramolecular hydrogen bonding of Chi-g-PAM was the dominant factor affecting its water solubility. While the grafting rate of Chi-g-PAM increased from 100% to 250%, the RDF of Chi-g-PAM decreased from 5.39 to 3.57 between O-H at 2.0 Å and 2.60 to 1.30 between N-H at 2.1 Å. The interaction between Chi-g-PAM and water increased with grafting rate as the absolute value of ΔGSFE for Chi-g-PAM increased from 432.917 kcal/mol to 858.749 kcal/mol. The solubility of Chi-g-PAM in acidic solution was much better than that of Chi-g-PAM in aqueous solution. Our work on the fundamental insights into the effect of grafted molecular structure of chitosan-based copolymer on its solubility will benefit the development of environmentally friendly chitosan-based flocculants.

Functional Materials Made by Combining Hydrogels (Cross-Linked Polyacrylamides) and Conducting Polymers (Polyanilines)-A Critical Review

Hydrogels made of cross-linked polyacrlyamides (cPAM) and conducting materials made of polyanilines (PANIs) are both the most widely used materials in each category. This is due to their accessible monomers, easy synthesis and excellent properties. Therefore, the combination of these materials produces composites which show enhanced properties and also synergy between the cPAM properties (e.g., elasticity) and those of PANIs (e.g., conductivity). The most common way to produce the composites is to form the gel by radical polymerization (usually by redox initiators) then incorporate the PANIs into the network by oxidative polymerization of anilines. It is often claimed that the product is a semi-interpenetrated network (s-IPN) made of linear PANIs penetrating the cPAM network. However, there is evidence that the nanopores of the hydrogel become filled with PANIs nanoparticles, producing a composite. On the other hand, swelling the cPAM in true solutions of PANIs macromolecules renders s-IPN with different properties. Technological applications of the composites have been developed, such as photothermal (PTA)/electromechanical actuators, supercapacitors, movement/pressure sensors, etc. PTA devices rely on the absorption of electromagnetic radiation (light, microwaves, radiofrequency) by PANIs, which heats up the composite, triggering the phase transition of a thermosensitive cPAM. Therefore, the synergy of properties of both polymers is beneficial.

Binding of Anionic Polyacrylamide with Amidase and Laccase under 298, 303, and 308 K: Docking and Molecular Dynamics Simulation Studies Combined with Experiments

Amidase and laccase play a key role in the degradation process of anionic polyacrylamide (HPAM). However, the largest challenge of HPAM enzymatic degradation is whether the enzyme can bind with a substrate for a period of time. Here, the most suitable complexes, namely, Rh Amidase-HPAM-2 and Bacillus subtilis (B. subtilis) laccase-HPAM-3, were obtained by docking, and they were carried out for molecular dynamics simulation (MDS) under 298, 303, and 308 K. MDS result analysis showed that Rh Amidase-HPAM-2 was the most stable at 298 K mainly due to a salt bridge and a hydrogen bond, and B. subtilis laccase-HPAM-3 was the most stable at 298 K mainly due to two electrostatic and hydrogen bonds. The LYS96 in Rh Amidase-HPAM-2 and LYS135 in B. subtilis laccase-HPAM-3 had been the most important in their binding process. The binding of Rh Amidase-HPAM-2 and B. subtilis laccase-HPAM-3 was optimal at 303 and 298 K, respectively. HPAM was degraded by mixed bacteria, and the optimal conditions were determined to be 308 K, initial pH = 7, and an inoculated dosage of 2 mL. Under these conditions, the degradation ratio reached 39.24%. The effect of parameters on the HPAM degradation ratio followed a decreasing order of temperature > initial pH > inoculated dosage. The HPAM codegradation mechanism was supposed by mixed bacteria according to test data. The mixed bacteria secreted both amidase and laccase, and they interacted jointly with HPAM. These results lay a theoretical foundation to design and modify the enzyme through mutation experiments in the future.

A Review on Coagulation/Flocculation in Dewatering of Coal Slurry

Coal slurry is an essential component of mining operations, accounting for more than half of operating costs. Dewatering technology is simultaneously confronted with obstacles and possibilities, and it may yet be improved as the crucial step for reducing the ultimate processing cost. Coagulation/flocculation is used as a dewatering process that is reasonably cost-effective and user-friendly. This paper reviews application of different coagulants/flocculants and their combinations in dewatering mechanisms. In this context, various polymeric flocculants are discussed in the coal slurry in depth. Many operational parameters that influence the performance of coal slurry flocculation are also presented. Furthermore, a discussion is provided on the mechanism of flocculants’ interaction, the strategy of combining flocculants, and efficient selection methods of flocculants. Finally, coagulation/flocculation remaining challenges and technological improvements for the better development of highly efficient treatment methods were highlighted, focusing on the intricate composition of slurry and its treatment difficulties.

Co-transport of negatively charged nanoparticles in saturated porous media: Impacts of hydrophobicity and surface O-functional groups

Graphene oxide (GO) and polystyrene nanoplastic (PSNP) are typical carbonaceous nanomaterials which likely co-exist in soil and sediment. Here, we describe the transport of GO, irradiation reduced GO (RGO) and PSNP in saturated quartz sand both in single and binary systems. In the single transport system, the materials exhibited mobility in the order of GO > RGO > PSNP, due to increased hydrophobicity and decreased negative surface charges. Nevertheless, the co-transport of (R)GO and PSNP in the binary transport system was much more intricate. In Na⁺ saturated porous media, PSNP preferred to interact with (R)GO relative to the highly negatively charged quartz sand, thus (R)GO carried PSNP to break through the sand column. However, in Ca²⁺ saturated porous media, the transport of both (R)GO and PSNP was depressed, attributed to the particle-collector and particle-particle bridging effects between Ca²⁺ and the metal-complexing moieties of the nanoparticles and sand grains. Moreover, GO influenced the co-transport of PSNP to a larger extent than RGO, especially at relatively high ionic strength, because of the more abundant surface O-functional groups on GO providing more complexion sites with Ca²⁺. These results demonstrated that the transport of negatively charged nanomaterials was greatly related to the hydrophobicity and surface O-functional groups.

Effect of Dodecane-Oleic Acid Collector Mixture on the Evolution of Wetting Film between Air Bubble and Low-Rank Coal

The wetting film evolution process is essential for flotation, especially in bubble–particle attachment. A mixed collector has been proved effective in promoting flotation. In this paper, the effect of a mixed collector (MC) composed by n-dodecane (D) and oleic acid (OA) on wetting film evolution was investigated using the extended Derjagin–Landau–Verwey–Overbeek (EDLVO) theory, the Stefan–Reynolds model, induction time, and zeta potential measurement. The hydrophobic force constant between bubble and coal treated by different collectors was analyzed. The results showed that MC was superior in reducing the induction time and increasing the zeta potential. When bubbles interacted with coal treated by MC, they had relatively low interaction energy, high critical film thickness, and high drainage rate. The order of hydrophobic force constant was no reagent < D < OA < MC. It indicated that the hydrophobic interaction between bubbles and coal particles treated by MC was the strongest because of the synergistic effect of D and OA.

Biodegradation of anionic polyacrylamide mediated by laccase and amidase: docking, virtual mutation based on affinity and DFT study

The aim of this work was to document the elucidation of a mechanism as a reference.

Fine Migration Control in Sandstones: Surface Force Analysis and Application of DLVO Theory

Formation damage caused by fine migration and straining is a well-documented phenomenon in sandstone reservoirs. Fine migration and the associated permeability decline have been observed in various experimental studies, and this phenomenon has been broadly explained by the analysis of surface forces between fines and sand grains. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is a useful tool to help understand and model the fine release, migration, and control phenomena within porous media by quantifying the total interaction energy of the fine-brine-rock (FBR) system. Fine migration is mainly caused by changes in the attractive and repulsive surface forces, which are triggered by mud invasion during drilling activity, the utilization of completion fluid, acidizing treatment, and water injection into the reservoir during secondary and tertiary recovery operations. Increasing pH and decreasing water salinity collectively affect the attractive and repulsive forces and, at a specific value of pH, and critical salt concentration (CSC), the total interaction energy of the FBR system (V _T) shifts from negative to positive, indicating the initiation of fine release. Maintaining the system pH, setting the salinity above the CSC, tuning the ionic composition of injected water, and using nanoparticles (NPs) are practical options to control fine migration. DLVO modeling elucidates the total interaction energy between fines and sand grains based on the calculation of surface forces of the system. In this context, zeta potential is an important indicator of an increase or decrease in repulsive forces. Using available data, two correlations have been developed to calculate the zeta potential for sandstone reservoirs in high- and low-salinity environments and validated with experimental values. Based on surface force analysis, the CSC is predicted by the DLVO model; it is in close agreement with the experimental value from the literature. The critical pH value is also estimated for alkaline flooding. Model results confirm that the application of NPs and the presence of divalent ions increase the attractive force and help to mitigate the fine migration problem. Hence, a new insight into the analysis of quantified surface forces is presented in current research work by the practical application of the DLVO theory to model fine migration initiation under the influence of injection water chemistry.

pH-Triggered Interfacial Interaction of Kaolinite/Chitosan Nanocomposites with Anionic Azo Dye

Advanced engineering of naturally occurring materials opens new doors in nanoscience and nanotechnology for the separation and/or removal of environmental hazards. Here, a series of nanocomposites containing kaolinite and chitosan varying in the range of 20 to 80% (w/w) kaolinite were used for the adsorptive removal of a reactive textile dye, Remazol Red, from an aqueous solution. Batch experiments were carried out to investigate the effects of pH, contact time, and initial dye concentration on the adsorption capacity. Nanocomposites containing 80% kaolinite (w/w) and 20% chitosan (w/w), i.e., NK80C20, showed an equilibrium adsorption capacity of 371.8 mg/g at pH 2.5, which was 5.2 times higher than that of commercial activated charcoal. Moreover, NK80C20 was regenerated instantly up to 99.9% at pH 10. Therefore, NK80C20 can be effectively utilized as a potential adsorbent for the separation of Remazol Red and homologous azo dyes from industrial effluents. We expect that the findings from this study will play a vital role in environmental research leading to advanced applications in water purification.