In this work, we report the synthesis of two Schiff bases of substituted gallic acid derivatives via amidation reaction and their characterization using ¹H-NMR spectroscopy to study their inhibition performance on the aggressive attack of HCl on mild steel (MS). The inhibitive performance was examined using chemical (weight loss) and electrochemical (Tafel and EIS) test methods. The results indicate that these derivatives significantly suppress the dissolution rate of mild steel via adsorption phenomena, which correlates to the Langmuir adsorption model. Tafel data display the mixed-type properties of these compounds and EIS results show that increasing Schiff base concentration not only leads to delaying the charge transfer (R_ct) of iron from 26.4 ohm cm⁻² to 227.7 ohm cm⁻² but also decreases the capacitance of the adsorbed double layer (C_dl) from 8.58 (F cm⁻²) × 10⁻⁵ to 2.55 (F cm⁻²) × 10⁻⁵. The inhibition efficiency percentage reaches the peak (90%) at optimum concentration of 250 ppm. The Monte Carlo simulations confirm the adsorption ability of the as-prepared compounds on the Fe (1 1 0) crystal. The SEM/EDX results revealed the presence of a protective film on the mild steel sample.

Improving oil production for high-salinity reservoirs using polymer flooding is challenging due to chemical and mechanical degradations. This study developed two biodegradable biopolymers based on graft copolymerization of guar gum (GG) with two different co-monomers, which are acrylamide (Am) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and cross-linked by N,N′-methylene bisacrylamide (MBA) to face these challenges. The newly synthesized guar gum-based hydrogels, GG-g-poly(Am-AMPS) (GH) and GG-g-poly(Am-AMPS)/Biochar (GBH composite), were evaluated as potential candidates for enhanced oil recovery (EOR) under high-salinity conditions. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) of the synthesized hydrogels were investigated, and their rheological properties were measured at room temperature. Both GH and GHB display a shear-thinning performance. In polymer flooding experiments, guar gum hydrogel (GH) and guar gum/biochar composite hydrogel (GHB) showed a remarkable influence on delaying the water breakthrough and proved to be effective biopolymers for enhanced oil recovery in high-salinity reservoirs. At the optimum concentration of 5 g/L, GH flooding achieved maximum oil recoveries of 70.53 and 72.11% in secondary and tertiary recovery processes, respectively. Meanwhile, the waterflooding process achieved an ultimate oil recovery of 58.42%. GHB flooding at optimum concentration, 2 g/L, increased the amount of oil recovery by 8.95% in tertiary recovery compared to waterflooding. Furthermore, GH (5 g/L) and GHB (2 g/L) slightly enhanced the rock water wettability as confirmed by contact angle measurements for GH and the relative permeability saturation curves for GH and GHB.

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite’s structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite’s water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution’s acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process’s feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.