Cornelia Gertina Catharina Elizabeth van Sittert

Understanding the mechanism of enhanced charge separation and visible light photocatalytic activity of modified wurtzite ZnO with nanoclusters of ZnS and graphene oxide: from a hybrid density functional study

Recently, semiconductor photocatalysts have received significant interest in addressing the global energy and environmental crisis. Despite the great potential application of zinc oxide (ZnO), the utilisation efficiency of solar energy is limited only to the ultraviolet (UV) region. Therefore, our research interest is centred on the development of a model hybrid ZnO-based photocatalyst material with efficient photocatalytic performance and stability. A hybrid ternary ZnS/graphene oxide (GO)/ZnO system, where the band edges of the individual components in the heterostructure will have a step-wise structure for harvesting a broader portion of the solar spectrum, is an excellent solution. Herein, we explore the charge transfer, the improved photocatalytic mechanism, and the electronic and interfacial properties of the hybrid van der Waals (vdWs) ZnS/GO/ZnO heterostructure for the first time by carrying out comprehensive hybrid density functional theory calculations. Our results reveal the existence of vdWs interaction, enhance charge transfer, narrow the band gap and show remarkable improvement in the visible light photocatalytic activity of the heterostructures compared to pure ZnO. This enhancement is ascribed to the electron acceptor–transporter role played by the GO sheet in the interfacial layer of ZnS and ZnO. According to adhesion energy results, the monolayers are in contact and form stable heterostructures. The calculated charge density difference shows interlayer charge transfer from the ZnO(001) surface to the ZnS(110) surface through the GO sheet. Most significantly, the ZnS/GO/ZnO heterostructures exhibit a type-II band alignment, which significantly restrains the recombination of charge carriers. The band edge positions of ZnS/GO/ZnO with enough driving force for electron and hole transfer are well aligned for the feasibility of splitting water into H2 and O2, as well as for photodegrading pollutants in the water system. Therefore, the vdWs ZnS/GO/ZnO heterostructures appear as a new type of photocatalyst material for solar energy application. This study illustrates the usefulness of using low cost GO as an interfacial electron acceptor–donor to boost the photocatalytic performance of ZnO-based photocatalysts. The findings in this study provide a theoretical basis for developing highly efficient ZnO-based photocatalysts, as well as attract broad interest in VdWs heterostructure research in photocatalysis.

Towards a better understanding of alkene metathesis: elucidating the properties of the major metal carbene catalyst types

The difference in activity of metal carbene catalysts has a major influence on the efficiency and application of these metal carbenes as metathesis catalysts. The focus of this research is to examine the properties of the major metal carbene catalyst types to understand the general activity trend. A comparative investigation of the foremost Fischer-, Tebbe-, Grubbs-, and Schrock-type metal carbenes was done using a qualitative structure–activity type computational method via principal component analysis. The effect of the change in metal atom as well as the change in ligands was specifically considered. Four Fischer-, a Tebbe-, five Grubbs-, and a Schrock-type carbene were investigated in this regard. Geometry optimizations of all species were done at the GGA/PBE/DNP level with Materials Studio DMol3 and subsequent single-point energy calculations were done with Gaussian at the PBEPBE level with the cc-pVQZ-type basis sets. Results showed that the descriptors extracted by the principal component analyses could successfully reproduce or match the generalized trend for metathesis activity, highlighting the importance of the frontier orbitals in the metathesis reaction.Graphical Abstract

Improved Metathesis Lifetime: Chelating Pyridinyl-Alcoholato Ligands in the Second Generation Grubbs Precatalyst

Hemilabile ligands can release a free coordination site “on demand” of an incoming nucleophilic substrate while occupying it otherwise. This is believed to increase the thermal stability and activity of catalytic systems and therefore prevent decomposition via free coordination sites. In this investigation chelating pyridinyl-alcoholato ligands were identified as possible hemilabile ligands for incorporation into the second generation Grubbs precatalyst. The O,N-alcoholato ligands with different steric bulk could be successfully incorporated into the precatalysts. The incorporation of the sterically hindered, hemilabile O,N-ligands improved the thermal stability, activity, selectivity and lifetime of these complexes towards the metathesis of 1-octene. A decrease in the activity of the second generation Grubbs precatalyst was additionally observed after incorporating a hemilabile O,N-ligand with two phenyl groups into the system, while increasing their lifetime.

Role of MoS2 and WS2 monolayers on photocatalytic hydrogen production and the pollutant degradation of monoclinic BiVO4: a first-principles study

The global dependence on exhaustible fossil fuel resources has made the search for an alternative renewable and sustainable fuel more urgent. Photocatalysis has gained increasing consideration as a promising technology to solve problems associated with solar energy conversion. Fabricated m-BiVO4-based heterostructures have shown improved photocatalytic activity for hydrogen evolution and pollutant degradation; however, a deeper understanding of the photocatalytic mechanism and the role of the monolayers is still lacking. Moreover, no theoretical studies have been carried out on MS2/m-BiVO4(010) heterostructures. In the present study, the roles of MoS2 and WS2 monolayers loaded onto a m-BiVO4 surface for active photocatalytic hydrogen production and pollutant degradation are explored using first-principle studies. Herein, hybrid density functional calculations and a long-range dispersion correction method were used to investigate the charge transfer, electronic properties, photocatalytic activity and mechanism of the MS2/m-BiVO4(010) heterostructures. The results showed a narrow band gap, built-in potential and a type-II band alignment for the MS2/m-BiVO4(010) heterostructures compared to pure m-BiVO4, which favour the separation and transfer of charge carriers and visible-light-driven activity. The MoS2/m-BiVO4 heterostructure showed a suitable band edge for hydrogen production and pollutant degradation compared to the WS2/m-BiVO4 heterostructure. This improvement was attributed to the role of the MoS2 monolayer as an electron donor, the many reactive sites on the MoS2 surface and the enhanced electron/hole pair separation of charge carriers at the MoS2/m-BiVO4(010) interface. Considering that the MS2 monolayer coupled with m-BiVO4 can restrain the electron–hole recombination rate without lattice distortion indicates that the heterostructure approach is better than the doping approach. Based on the analysis of the electronic properties, the MS2/m-BiVO4(010) heterostructures were shown to fit within the acceptable band gap and built-in potential range. The proposed theoretical design paves a way for the effective and large-scale fabrication of m-BiVO4-based photocatalyst for solar energy conversion and environmental remediation applications.

A strategy for the synthesis of cyclomatrix-polyphosphazene nanoparticles from non-aromatic monomers

Cyclomatrix-polyphosphazenes (C-PPZs) are a new class of nanomaterials that have attracted significant interest owing to their unique inorganic–organic hybrid structure and tunable properties. The limited success that has been achieved in producing C-PPZs from non-aromatic organic monomers is ascribed to an insufficient understanding of their polymerization mechanism. In this work, by using a new strategy termed solubility-parameter-triggered polycondensation, we demonstrate experimentally and computationally that C-PPZs nanoparticle synthesis from non-aromatic monomers is feasible and solubility-parameter (SP)-dependent. The precipitation polycondensation of C-PPZ occurs once the solution SP is outside a critical SP range, while within the critical range only oligomers are detected from the reaction; this SP-dependent rule is applicable for C-PPZ oligomers from both aromatic and non-aromatic monomers. The upper/lower critical SP values increase with the increase of organic monomer hydrophilicity. The morphologies of C-PPZ products exist as clusters or nanoparticles when the reaction solvent SP is controlled below the upper critical SP or exceeds the lower critical SP, respectively. This theory presents a feasible way to predict and determine the precipitation polycondensation conditions and product morphology of any novel C-PPZ nanomaterial.