Enhanced photocatalytic activity of BiVO4 powders synthesized in presence of EDTA for the decolorization of rhodamine B from aqueous solution

Construction of MIL-125-NH2@BiVO4 Composites for Efficient Photocatalytic Dye Degradation

The design and construction of a photocatalyst with a heterostructure are a feasible and effective way to enhance the catalytic performance. Herein, a specially designed composite based on MIL-125-NH₂ and BiVO₄ was prepared and used for wastewater treatment. In the hybrid MIL-125-NH₂@BiVO₄, MIL-125-NH₂ was uniformly dispersed on the BiVO₄ surface. There is a high affinity between MIL-125-NH₂ and BiVO₄ due to the lattice defects. Under visible light irradiation, the catalytic activity of the as-prepared composite was evaluated by the degradation of various dyes such as malachite green, crystal violet, methylene blue, and Congo red. Nearly 98.7, 99.1, and 41.0% of the initial MG, MB and Cr(VI) were respectively removed over the optical sample of BVTN-5, demonstrating that the hybrid holds great promise for practical applications. Moreover, the composites can be recycled and reused with good stability after five consecutive cycles. The mechanism was proposed and discussed in detail. This work will shed light on the construction of MOF-based composites for efficient photocatalysis.

High-performance BiVO4 photoanodes cocatalyzed with bilayer metal-organic frameworks for photoelectrochemical application

In this work, we modified a BiVO₄ photoanode with bilayer Fe-MOF and Ni-MOF as cocatalysts for the first time and obtained a highly efficient BiVO₄ composite photoanode whose photocurrent density was increased by 2.7 times. The optimized BiVO₄/Fe-MOF/Ni-MOF photoanode demonstrated a photocurrent density of 1.80 mA/cm² at 1.23 V vs. a reversible hydrogen electrode (RHE). The onset potential of the BiVO₄/Fe-MOF/Ni-MOF photoanode markedly decreased from 0.9 V to 0.69 V in comparison with the pure BiVO₄ photoanode. It is speculated that Fe-MOF and Ni-MOF led to more reactive oxygen evolution sites and that the bilayer cocatalysts synergistically promoted the separation of photogenerated electron-hole pairs, which may be the influencing factor for the photoelectrochemical performance of the BiVO₄/Fe-MOF/Ni-MOF photoanode being distinctively enhanced. Thus, this work sheds some interesting new light on the construction of a high-efficiency photoanode for photoelectrochemical applications.

Adsorption and mass transfer studies of methylene blue onto comminuted seedpods from Luehea divaricata and Inga laurina

In this work, comminuted seedpods of the forest species Luehea divaricata (LDPR) and Inga laurina (ILPR) were used as alternative and environmental-friendly adsorbents for the methylene blue (MB) removal from aqueous solutions. Batch adsorption experiments were carried out at the native pH of the solution (pH = 8.7), with curves of removal and adsorption capacity crossed at 0.75 g L^-1, having 125 mg g^-1 for LDPR and 115 mg g^-1 for ILPR. The kinetic models of pseudo-first-order (PFO) and HSDM-Crank were the most adequate to represent MB dye concentration decay data for both biosorbents. The equilibrium curves were better adjusted by the Langmuir model for both adsorbents, with maximum adsorption capacity increased from 279 to 325 mg g^-1 for LDPR, and 199 to 233 mg g^-1 for ILPR, as a function of an increase in temperature from 298 to 328 K. The thermodynamic parameters showed that both systems are spontaneous with a dominance of physisorption. Mass transfer analysis indicates that the external mass transfer is the limiting step, with Bi < 0.5. Surface diffusion increased with the adsorption capacity, presenting linear and exponential behavior for the ILPR and PLPR adsorbents, respectively. Both materials proved to be efficient in treating a simulated effluent with similar industrial wastewater characteristics, reaching superior values at 70% of color removal.

Monoclinic-tetragonal-monoclinic phase transitions in Eu0.1Bi0.9VO4 under pressure

The promising technological material Eu_0.1Bi_0.9VO₄, has been studied for the first time at room-temperature under high-pressure, up to 24.9 GPa, by means of in situ angle dispersive powder x-ray diffraction (XRD). The compound undergoes two phase transitions at 1.9 and 16.1 GPa. The first transition is from the monoclinic fergusonite-type structure (space group I2/a) to a tetragonal scheelite-type structure (space group I4₁/a), being a ferroelastic-paraelastic transformation similar to that previously reported for isomorphic pristine BiVO₄. The second phase transition is first-order in nature. The scheelite-type and the second high-pressure phase coexist in a wide pressure range. A monoclinic structure (space group P2₁/n) is proposed for the second high-pressure phase. Both transitions are reversible upon decompression. Details of the different crystal structures are reported. All the three observed structures are composed of network of VO₄ tetrahedra and BiO₈ (or EuO₈ due to the substitution of Bi by Eu) dodecahedra. The room-temperature P-V equation of state and axial anisotropic compressibilities of the fergusonite and scheelite polymorphs are also given. In particular, the isothermal compressibility tensor for the monoclinic fergusonite phase has been calculated.