Comparative Study on Lipases Immobilized onto Bentonite and Modified Bentonites and Their Catalytic Properties

The hydrophobic property and structure of Na-bentonite (Na-bent) were tuned by intercalation with cationic surfactants for lipase adsorption. The adsorption isotherms of lipase on Na-bent and modified bentonites demonstrated Langmuir-type shape, and Na-bent showed higher adsorption efficiency than modified bentonites. The observed overlap of lipase molecules on the support and the interactions between these molecules under high protein loading caused the reduction in the activity of immobilized lipase. The immobilized lipases on modified bentonites (Bent-DTAB-lipase, Bent-CTAB-lipase, and Bent-OTAB-lipase) exhibited higher catalytic activity than that on Na-bent, due to the hydrophobically interfacial activation of modified bentonites toward lipase. The highest catalytic activity and stability were observed on Bent-CTAB-lipase, resulting from the tunable hydrophilic/hydrophobic balance of the support’s surface, while the excessive hydrophobic property showed negative influence on lipase’s catalytic performance. The immobilized lipases onto modified bentonites with hydrophobic property showed higher thermal stability and reusability than Na-bent-lipase

Decontamination of Sr(II) on Magnetic Polyaniline/Graphene Oxide Composites: Evidence from Experimental, Spectroscopic, and Modeling Investigation

The interaction of Sr­(II) on magnetic polyaniline/graphene oxide (PANI/GO) composites was elucidated by batch, EXAFS, and surface complexation modeling techniques. The batch experiments showed that decreased uptake of Sr­(II) on magnetic PANI/GO composites was observed with increasing ionic strength at pH <5.0, whereas no effect of ionic strength on Sr­(II) uptake was shown at pH >5.0. The maximum uptake capacity of magnetic PANI/GO composites derived from the Langmuir model at pH 3.0 and 293 K was 37.17 mg/g. The outer-sphere surface complexation controlled the uptake of Sr­(II) on magnetic PANI/GO composites at pH 3.0 due to the similarity to the EXAFS spectra of Sr²⁺ in aqueous solutions, but the Sr­(II) uptake at pH 7.0 was inner sphere complexation owing to the occurrence of the Sr–C shell. According to the analysis of surface complexation modeling, uptake of Sr­(II) on magnetic PANI/GO composites was well simulated using a diffuse layer model with an outer-sphere complex (SOHSr²⁺ species) and two inner-sphere complexes (i.e., (SO)₂Sr­(OH)⁻ and SOSr⁺ species). These findings are crucial for the potential application of magnetic nanomaterials as a promising candidate for the uptake of radionuclides for environmental remediation

Weak-Bond-Based Photoreduction of Polybrominated Diphenyl Ethers on Graphene in Water

The photoreduction of polybrominated diphenyl ethers (PBDEs)a kind of persistent organic pollutants with high hydrophobicitywas achieved on graphene in aqueous solution. We first observed that reduced graphene oxide (RGO) exhibited higher reaction rate than graphene oxide (GO). FT-IR and elementary analysis indicated that GO first was reduced to RGO at the beginning of the irradiation, and RGO is the real photoactive species. The theoretical calculations and adsorption experiments reveal a new photochemical debromination pathway based on the weak interaction, such as hydrophobic interaction, π–π interaction, and halogen-binding interaction between the PBDEs and RGO. These interactions enable the photoinduced electron transfer from the RGO to PBDEs and lead to the efficient reductive debromination of PBDEs. This study provides a green and low-cost method for removal of the high hydrophobicity halogen organic pollutants in water with environmentally benign carbon nanomaterials

Glycerol-Modified Binary Layered Double Hydroxide Nanocomposites for Uranium Immobilization via Extended X‑ray Absorption Fine Structure Technique and Density Functional Theory Calculation

Novel, efficient, glycerol-modified nanoscale layered double hydroxides (rods Ca/Al LDH-Gl and flocculent Ni/Al LDH-Gl) were successfully synthesized by a simple one-step hydrothermal synthesis route and showed excellent adsorption capacities for U­(VI) from aqueous solutions under various environmental conditions. The advanced spectroscopy analysis confirmed the existence of abundant oxygen-containing functional groups (e.g., C–O, O–CO, and CO) on the surfaces of Ca/Al LDH-Gl and Ni/Al LDH-Gl, which could provide enough free active sites for the binding of U­(VI). The maximum adsorption capacities of U­(VI) calculated from the Sips model were 266.5 mg·g^–1 for Ca/Al LDH-Gl and 142.3 mg·g^–1 for Ni/Al LDH-Gl at 298.15 K, and the higher adsorption capacity of Ca/Al LDH-Gl might be due to more functional groups and abundant high-activity “Ca–O” groups. Macroscopic experiments proved that the interaction of U­(VI) on Ca/Al LDH-Gl and Ni/Al LDH-Gl was due to surface complexation and electrostatic interactions. The extended X-ray absorption fine structure analysis confirmed that U­(IV) did not transformation to U­(VI) on solid particles, and stable inner-sphere complexes were not formed by reduction interaction but by chemical adsorption. The density functional theory (DFT) calculations further evidenced that the higher adsorption energies (i.e., <i>E</i>_ad = 4.00 eV for Ca/Al LDH-Gl-UO₂²⁺ and <i>E</i>_ad = 2.43 eV for Ca/Al LDH-Gl-UO₂CO₃) were mainly attributed to stronger hydrogen bonds and electrostatic interactions. The superior immobilization performance of Ca/Al LDH-Gl supports a potential strategy for decontamination of UO₂²⁺ from wastewater, and it may provide new insights for the efficient removal of radionuclides in environmental pollution cleanup

Oxygen-Vacancy-Activated CO₂ Splitting over Amorphous Oxide Semiconductor Photocatalyst

Gaseous oxides generated during industrial processes, such as carbon oxides (CO_<i>x</i>) and nitrogen oxides (NO_<i>x</i>), have important effects on the Earth’s atmosphere. It is highly desired to develop a low-cost and efficient route to convert them to harmless products. Here, direct splitting of gaseous oxides was proposed on the basis of photocatalysis by an amorphous oxide semiconductor. As an example, splitting of CO₂ into carbon and oxygen was achieved over amorphous zinc germanate (α-Zn-Ge-O) semiconductor photocatalyst under 300 W Xe lamp irradiation. Electron paramagnetic resonance and ¹⁸O isotope labeling indicated that the splitting of CO₂ was achieved via photoinduced oxygen vacancies on α-Zn-Ge-O reacting and thus filling with O of CO₂, while the photogenerated electrons reduced the carbon species of CO₂ to solid carbon. Under irradiation, such a defect reaction is sustainable by continuous photogenerated hole oxidation of surface oxygen atoms on α-Zn-Ge-O to form oxygen vacancies and to release O₂. When we used H₂O or NO in place of CO₂, H₂ and O₂ or N₂ and O₂ were evolved, respectively, indicating the same mechanism can also split H₂O or NO