Narrow Results

The contamination of aquatic systems by tetracycline hydrochloride (TC) has emerged as an urgent environmental concern necessitating immediate intervention. Herein, a mechanochemical approach was utilized to synthesize a FeOOH@AC nanocomposite through the co-grinding of goethite (FeOOH), hydroxylamine hydrochloride (NH₂OH⋅HCl), and activated carbon (AC). The FeOOH@AC nanocomposite acted as a catalyst for the activation of sodium persulfate (PS), producing strong oxidizing radicals for the removal of TC from water. The results demonstrated that the physicochemical properties and crystal structure of FeOOH were altered via ball-milling treatment. The activation of PS-generated sulfate radicals (SO${}_4^{\cdot -})$ and hydroxyl radicals (${}^{\cdot }$OH) synergistically degraded TC. Additionally, the degradation rate of TC in a 50mg/L solution reached 91.26% after the addition of FeOOH@AC and PS. This work offers a theoretical and technical foundation for the mechanochemical ball milling preparation of FeOOH@AC, facilitating PS activation for the degradation of TC in water.

The electronic structure of S adsorption on goethite (110) surface has been studied by ASED-MO cluster calculations. For S location, the most exposed surface atoms of goethite surface were selected. The calculations show that the surface offers several places for S adsorption. The most energetically stable system corresponds to S location above H atom.

We studied in detail the configurations that correspond to the higher OP values. For these configurations, the H-S and Fe-S computed distances are 2.1 and 3.7 Å, respectively. The H-S and Fe-S are mainly bonding interaction with OP values of 0.156 and 0.034, respectively. The Fe-S interaction mainly involves Fe 3d_x2-y2 atomic orbitals with lesser participation of Fe 4p_y and Fe 3d_yz atomic orbitals. The O-S interaction shows the same bonding and antibonding contributions giving a small OP value. The O-S interaction involves O 2p orbitals. There is an electron transfer to the Fe atom from the S atom. On the other hand, there is an electron transfer to S atom from the H and O atoms, respectively.

The electronic structure of H₂S adsorbed on the goethite (110) surface has been studied by ASED-MO cluster calculations. We have studied both the perpendicular and the parallel H₂S molecular adsorption on the FeOOH(110) surface. We have analyzed the adsorption configuration energies including rotation. The parallel species does not rotate during adsorption and corresponds to the most stable configuration. We have also studied the bonding contributions for the minimum energy configuration and the density of states plots.

The decomposition of goethite and goethite/siderite concentrates into hematite with thermal modification was studied through the measurements of X-ray diffraction (XRD), scanning electronic microscope (SEM) and thermal gravimetric analysis (TGA). The experimental results showed that goethite decomposed into hematite directly at around 300°C without any intermediate phase and the decomposition of siderite completed at 500°C. Nanoscale granular structures were observed in the thermally treated products. It deserves highlighting that the decomposition processes proceeded from surfaces into bulks.