Study on the influence of lattice integrity and phase composition to the photocatalytic efficiency of ZnS material

Different Crystal Forms of ZnS Nanomaterials for the Adsorption of Elemental Mercury

ZnS is a promising sorbent in recovering Hg⁰ from industrial flue gas due to its excellent Hg⁰ adsorption capacity. However, the internal structure-activity relationship still needs to be further clarified. In this work, ZnS sorbents with different structures were synthesized with the hydrothermal method by tuning the temperature. The samples had significant differences in the crystallinity, morphology, particle size, and sulfur (S) active sites. The results indicated that Hg⁰ removal performance was determined by the specific surface area and S active sites. ZnS synthesized at low temperatures (80-ZnS and 120-ZnS) had a larger surface area, while the S sites on the high-temperature-synthesized sample (160-ZnS) were more active for Hg⁰ adsorption. The 160-ZnS sample exhibited a much higher Hg⁰ adsorption amount per unit surface area. Further characterization revealed that S₂^2- and S_x were the main active sites for Hg⁰ adsorption. S_x existed in the form of long-chain polysulfur (L-S_x) on 80-ZnS and 120-ZnS, while it exhibited in the form of short-chain polysulfur (S-S_x) on 160-ZnS. L-S_x had negligible adsorption ability, while S-S_x had a high affinity for Hg⁰. Hg⁰ can react with S₂^2- and S-S_x, forming α-HgS and β-HgS, respectively. The new insight in this work can provide theoretical guidance for the design and structure optimization of ZnS, facilitating its practical industrial application.

The hydrothermal evolution of the phase and shape of ZnS nanostructures and their gas-sensing properties

The evolution of the phase of ZnS was achieved by adjusting the hydrothermal holding time or the dosage of the surfactant.

Photocatalyzed Reduction of Bicarbonate to Formate: Effect of ZnS Crystal Structure and Positive Hole Scavenger

Zinc sulfide is a promising catalyst due to its abundance, low cost, low toxicity and conduction band position that enables the photoreduction of CO2 to formic acid. This study is the first to examine experimentally the photocatalytic differences between wurtzite and sphalerite under the parameters of size (micrometer and nanoscale), crystal lattice, surface area, and band gap on productivity in the photoreduction of HCO3(-). These photochemical experiments were conducted under air mass coefficient zero (AM 0) and AM 1.5 solar simulation conditions. We observed little to no formate production under AM 1.5, but found linear formate production as a function of time using AM 0 conditions. Compared to earlier reports involving bubbled CO2 in the presence of bicarbonate, our results point to bicarbonate as the species undergoing reduction. Also investigated are the effects of three hydroxylic positive hole scavengers, ethylene glycol, propan-2-ol (isopropyl alcohol, IPA) and glycerol on the reduction of HCO3(-). Glycerol, a green solvent derived from vegetable oil, greatly improved the apparent quantum efficiency of the photocatalytic reduction.

Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light

Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH₄ added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H₂ production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH₄ in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H₂ production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

Enhanced photocatalytic hydrogen production activities of Au-loaded ZnS flowers

Au-nanoparticle-decorated ZnS nanoarchitectures were fabricated by a simple hydrothermal approach combined with a deposition-precipitation method. After the deposition-precipitation process, 5-nm Au nanoparticles were homogeneously dispersed on the ZnS surface. In addition, the band gap of ZnS was also narrowed by the incorporation of a small amount of Au(I) ions. The photocatalytic hydrogen production activities of all the samples were evaluated by using Na(2)S and Na(2)SO(3) as sacrificial reagents in water under a 350 W xenon arc lamp. The results show that the photocatalytic hydrogen production rate of ZnS nanoarchitectures can be significantly improved by loading Au cocatalysts and reaches an optimal value (3306 μmol h(-1) g(-1)) at the Au content of 4% wt. Although strong surface plasmon resonance (SPR) absorption of the Au nanoparticles was found in the Au-loaded samples, all of these samples exhibit no activities in the visible light region (λ > 420 nm). On the basis of this Au/ZnS system, the possible roles of Au deposition in improving the photocatalytic hydrogen production activity, especially the necessary condition for SPR effect of metal nanostructures to function in the visible-light photocatalysis, are critically discussed.

Influence of lattice integrity and phase composition on the photocatalytic hydrogen production efficiency of ZnS nanomaterials

Ambient S annealing was adopted to regulate the crystallinity of a ZnS microsphere, which resulted in a significant improvement in the photocatalytic hydrogen production activity (PHPA). Moreover, with S ambient treatment, wurtzite ZnS showed better PHPA than sphalerite ZnS, possibly because the inter-polar electric field of the wurtzite phase could promote the separation of photo-excited electron-hole pairs.