Green synthesis, characterization, and application of Fe3O4 nanoparticles for methylene blue removal: RSM optimization, kinetic, isothermal studies, and molecular simulation.

Methylene Blue (MB) is a cationic dye causing various health problems such as asthma, heartbeat, eye and skin irritation, nausea, and distress during prolonged exposure. In this regard, the green magnetite nanoparticle was synthesized using the extract of Prosopis farcta. The synthesized Fe3O4nanoparticle was characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transforms Infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). The corresponding parameters, including the primary concentration of MB (5-65 mg/L), the dose of synthesized nanoparticle (0.025-0.925 g/L), solution pH (3-11), and contact time (20-60 min), were considered. Also, central composite design (CCD), as one of the response surface methodologies (RSM), was used for the related modelling and optimization. The particle size of the adsorbent was between 5 and 70 nm, and the nanoparticle has 206.75 m2/g of a specific surface, 6.1 nm of average pore size, and 0.3188 cm3/g of the total pore volume. The optimal conditions for MB removal by the nanoparticle were found to follow an initial MB concentration of 20 mg/L, 0.7 g/L of the nanoparticle dose, pH = 9, and a contact time of 50 min. The pseudo-second-order (PSO) and Freundlich models were the best kinetic and isothermal models for MB removal by the synthesized nanoparticle. Molecular modelling was used to optimize the MB molecular configuration and compute HOMO-LUMO energies, quantum-chemical descriptors, and molecular electrostatic potential to evaluate the nature reactivity of the MB molecule.

An experimental study of the effects of bacteria on asphaltene adsorption and wettability alteration of dolomite and quartz.

The adsorption of asphaltene on the rock surface and the changes in its wettability are very relevant issues in flow assurance and oil recovery studies, and for carbonate reservoirs, they are even more important. During microbial enhanced oil recovery (MEOR) processes, wettability alteration is considered a crucial mechanism leading to improved oil recovery. Therefore, it is essential to understand the mechanisms of surface wettability changes by bacteria and biosurfactants and find new and reliable methods to prevent asphaltene adsorption. Hence, the main aim of this research was to investigate the effect of a mixture of thiobacillus thiooxidans and thiobacillus ferooxidans microorganisms with an optimum effective temperature of around 30 °C (referred to as mesophilic bacteria), as well as a mixture of two moderate thermophiles Sulfobacillus thermosulfidooxidans for operating temperatures around 50 °C (referred to as moderately thermophilic bacteria) on the adsorption of asphaltene samples isolated from two different crude oils onto main reservoir minerals (i.e., quartz and dolomite). The results indicated that after two weeks of mineral aging in moderate thermophilic bacteria, the adsorption of asphaltene on both minerals increased between 180 and 290%. Fourier-transform infrared spectroscopy (FTIR) analysis for quartz and dolomite samples demonstrated that after aging in bacterial solution, bonds related to the adsorption of bacterial cells and biosurfactant production appear, which are the main factors of change in wettability. Alteration in wettability towards hydrophilicity expands hydrogen bonds on the surface, thus improving asphaltene adsorption due to polar interaction. Asphaltene 1 changed the contact angle of dolomite from 53.85° to 90.51° and asphaltene 2 from 53.85° to 100.41°. However, both strains of bacteria caused a strong water-wetting effect on the dolomite rock samples. The influence of moderate thermophilic bacteria on surface wettability is more significant than that of mesophilic bacteria, which may be caused by the high protein content of these bacteria, which expands hydrogen bonding with the surface. Adsorption of asphaltenes on dolomite rocks previously aged with bacteria showed that the wetted rock samples retained their water-wet state. This study highlights the dual impact of the used microorganisms. On one hand, they significantly reduce contact angles and shift wettability towards a strongly water-wet condition, a crucial positive factor for MEOR. On the other hand, these microorganisms can elevate the adsorption of asphaltenes on reservoir rock minerals, posing a potential challenge in the form of formation damage, particularly in low-permeability reservoirs.