In this study, pillared layered clays were prepared by modifying Vietnamese bentonite with polymeric Al and Fe. The obtained materials were characteristic of X-ray diffraction analysis, thermal analysis, and nitrogen adsorption/desorption isotherms. The results indicated that hydroxy-aluminum ([Al13O4(OH)24(H2O)12]7+) and poly-hydroxyl-Fe or polyoxo-Fe cations were intercalated into layers of clay, resulting in an increase of d001 values and of the specific surface areas compared with those of initial bentonite. Modified bentonites were employed to adsorb As(V) from aqueous solution. The adsorption of As(V) was strongly dependent on solution pH, and the maximum adsorption of modified bentonites was obtained in the pH 3.0 for Fe-bentonite and the pH 4.0 for Al-bentonite. The equilibrium adsorption study showed that the data were well fit by the Langmuir isotherm model. The maximum monolayer adsorption capacity of As(V) at 30°C derived from the Langmuir equation was 35.71 mg/g for Al-bentonite and 18.98 mg/g for Fe-bentonite. Adsorption kinetics, thermodynamics, and reusability of modified bentonites have been addressed.

In the present work, the modified bentonites were prepared by the modification of bentonite with cetyltrimethylammonium bromide (CTAB), both cetyltrimethylammonium bromide and hydroxy-Fe cations and both cetyltrimethylammonium bromide and hydroxy-Al cations. X-ray diffraction (XRD), thermal analysis (TG-DTA), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption/desorption isotherms were utilized to characterize the resultant modified bentonites. The modified bentonites were employed for the removal of phenol red dye from aqueous solution. Phenol red adsorption agreed well with the pseudo-second-order kinetic model. The equilibrium data were analyzed on the basis of various adsorption isotherm models, namely, Langmuir, Freundlich, and Dubinin‒Radushkevich models. The highest monolayer adsorption capacity of phenol red at 30°C derived from the Langmuir equation was 166.7 mg·g−1, 125.0 mg·g−1, and 100.0 mg·g−1 for CTAB‒bentonite, Al‒CTAB‒bentonite, and Fe‒CTAB‒bentonite, respectively. Different thermodynamic parameters were calculated, and it was concluded that the adsorption was spontaneous (∆G° < 0) and endothermic (∆H° > 0), with increased entropy (∆S° > 0) in all the investigated temperature ranges.

Herein, the single-atom Ni site heterogeneous catalysts supported by the UiO-66 structure (University of Oslo-66 metal organic framework) were successfully synthesized by a postsynthetic metalation method, where Ni ions are covalently attached to the missing-linker defect sites at zirconium oxide clusters (Zr6O4(OH)4) in as-prepared UiO-66 structure, [Zr6O4(OH)4(BDC)(DMF)10(OH)10] (BDC (benzene-1,4-dicarboxylate), DMF (dimethylformamide)). The structure properties of the catalysts were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption isotherms (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). It was found that single-atom Ni heterogeneous catalysts supported by the UiO-66 structure, UiO-66/Ni1.0 [Zr6O4(OH)4(C8H4O4)(DMF)10(OH)8Ni2(OH)2(Cl)2], showed a sphere-like morphology with a high specific surface area as well as good thermal stability. Specifically, the as-prepared UiO-66/Ni1.0 exhibited the excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy ( E a = 23.15   kJ   mo l − 1 ), high turnover frequency (76.19 molecules g-1 min-1), and high apparent rate constant ( k app = 0.956 mi n − 1 ). In addition, methylene blue (MB) was also chosen as the organic dye model for catalytic reduction reaction. The k app and TOF for the reduction of MB using UiO-66/Ni1.0 were 0.787 min−1 and 33.89 × 10 20 molecules g−1 min−1, respectively.

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CdMoO₄/g-C₃N₄/GO composites were first synthesized by a hydrothermal process for the photocatalytic degradation of rhodamine B (RhB) under visible light illumination. The findings show that CdMoO₄ is highly dispersed onto g-C₃N₄ and graphene oxide (GO) sheets. The surface area of the composite increased 27–30.5 times that of CdMoO₄, and its band gap energy decreased by about 1.26 times. These features significantly improve the photocatalytic activity of the composite in the RhB decomposition reaction under visible light. The RhB degradation efficiency of the CdMoO₄/g-C₃N₄/GO composite is 5.7, 1.36, and 1.65 times that of CdMoO₄, CdMoO₄/g-C₃N₄, and CdMoO₄/GO composites, respectively. The active species trapping experiments show that the main forms in RhB degradation are •O₂^– , •OH, and <i>h</i>⁺. The stability of the photocatalyst is retained even after the 5th reuse. In addition, RhB degradation products were identified with the high-performance liquid chromatography-mass spectrometry method, and the pathway of photocatalytic degradation was also addressed.