Department of Physical and Technical Sciences

The current study evaluated the innovative application of membrane distillation crystallization (MDCr) for dual treatment and resource recovery from acid mine drainage (AMD), a persistent environmental crisis in South African. This AMD was characterized by exorbitant concentrations of Ca2+ (2622 mg·L−1), Fe2+ (1421 mg·L−1), SO42−(9790 mg·L−1) and Cl− (1113 mg·L−1). The current study evaluated the performance of hollow fibre polypropylene membrane in processing both acidic (pH 3.58) and neutralized (pH 6.47) feedwaters. The permeate was 3.3 kg·m−2·h−1, 2.2 kg·m−2·h−1 and 1.3 kg·m−2·h−1 at 70, 60 and 50 °C respectively, which remained relatively stable at high recovery factors ( >80%). Acidic AMD promoted formation of large metal-rich ettringite and halite crystals while neutralized AMD produced small and dense ettringite, hexahydrite and jarosite crystals. This study highlighted the dual functionality of MDCr in water treatment and mineral resource recovery, offering a sustainable solution to address the AMD pollution crisis in South Africa.

Lateral 3D/2D perovskite heterostructures, which combine the high efficiency of 3D phases with the stability of 2D structures, have shown great potential in energy and optoelectronic applications. However, the ion migration dynamics driving their formation and stability remain unclear. Here, we use fluorescence microscopy to investigate the anisotropic migration of A-site cation methylammonium (MA+) and formamidinium (FA+) in phenylethylammonium lead bromide (PEA2PbBr4) nanoplatelets. We demonstrate that edge-initiated, preferential in-plane migration of these cations leads to the lateral growth of 3D domains at the edge of nanoplates, forming lateral 3D/2D perovskite heterostructures. FA+ migrates more slowly than MA+ due to the relatively large steric hindrance, suppressing the formation of transient quasi-2D phases and enhancing the phase purity and structural stability of the heterostructures. These results highlight the importance of cation selection and interface design in optimizing ion migration dynamics, offering key insights into improving the stability and performance of 3D/2D perovskite-based optoelectronic devices.

The significant threat posed by dye wastewater has driven the development of efficient adsorbents, such as metal organic frameworks (MOFs). Specifically, we explore the synthesis and application of ZnCo-based bimetallic zeolite imidazolate frameworks with a macro-microporous structure (SOM-ZnCo-ZIF), which exhibit enhanced adsorption capacity for dyes due to their large specific surface area and ordered porous arrangement. When SOM-ZnCo-ZIF is immersed in DMA solutions of methylene blue, methyl orange, crystal violet, and rhodamine B, due to its high specific surface area and the synergistic effect of ZnCo bimetallic clusters, SOM-ZnCo-ZIF significantly enhances dye adsorption. Notably, its adsorption capacity for Rhodamine B reaches an impressive 6798.9 mg/g, and within just 1 min, 0.5 g/L of SOM-ZnCo-ZIF can remove over 97% of Rhodamine B from a 60 mg/L solution. Moreover, it maintained a 92.8% dye removal efficiency in ten cycles without regeneration, demonstrating the effective adsorption capacity of SOM-ZnCo-ZIF. Density functional theory calculations have shown that the adsorption energy of ZnCo bimetallic ZIF for Rhodamine B is approximately twice that of a single metal. SOM-ZnCo-ZIF exhibits strong adsorption of Rhodamine B mainly due to its macro-microporous structure, which provides larger pore sizes (∼250 nm) allowing the dye molecules to infiltrate the porous network, and its ability to facilitate π-π stacking interactions between the benzene rings of Rhodamine B and the imidazole rings of the ZIF. Additionally, the interaction is further enhanced by strong coordination bonds and electrostatic interactions between the cationic dye and the negatively charged framework. This work not only proposes an effective adsorbent to remove Rhodamine B but also provides valuable insights for the rational design and synthesis of environmentally sustainable MOF structures.

Imidazolium based receptors selectively recognize anions, and have received more and more attention. In 2006 and 2010, we reviewed the mechanism and progress of imidazolium salt recognition of anions, respectively. In the past ten years, new developments have emerged in this area, including some new imidazolium motifs and the identification of a wider variety of biological anions. In this review, we discuss the progress of imidazolium receptors for the recognition of anions in the period of 2010-2019 and highlight the trends in this area. We first classify receptors based on motifs, including some newly emerging receptors, as well as new advances in existing receptor types at this stage. Then we discuss separately according to the types of anions, including ATP, GTP, DNA and RNA.

Understanding the mechanisms for nanoparticle nucleation and growth is crucial for the development of tailormade nanomaterials. Here, we use X-ray total scattering and Pair Distribution Function analysis to follow the formation and growth of niobium oxide nanoparticles. We study the solvothermal synthesis from niobium chloride in benzyl alcohol, and through investigations of the influence of reaction temperature, a formation pathway can be suggested. Upon dissolution of niobium chloride in benzyl alcohol, octahedral [NbCl6−xOx] complexes form through exchange of chloride ligands. Heating of the solution results in polymerization, where larger clusters built from multiple edge-sharing [NbCl6−xOx] octahedra assemble. This leads to the formation of a nucleation cluster with the ReO3 type structure, which grows to form nanoparticles of the Wadsley–Roth type H-Nb2O5 structure, which in the bulk phase usually only forms at high temperature. Upon further growth, structural defects appear, and the presence of shear-planes in the structure appears highly dependent on nanoparticle size.

Metabolic systems form the very foundation of life and as such are broadly taught in the molecular life sciences. Here, we describe the biochemistry educator community-based development and use of an assessment instrument designed to evaluate students’ ideas about metabolic pathway dynamics and regulation in undergraduate biochemistry courses. Analysis of student responses showed that most students were able to interpret visual representations in an unfamiliar metabolic pathway and that many could make basic predictions about how the system would be expected to respond to changes. However, fewer students generated nuanced responses that accounted for both microscopic changes at the protein level and macroscopic changes in pathway product outputs. These findings identify some of the challenges of meaningfully assessing students’ understanding of metabolic pathways and could inform how instructors think about teaching and assessing metabolism in undergraduate biochemistry and beyond. The results also suggest future avenues for biochemistry education research.

A facile route to 4,4'-bipyrazole (H2bpz) and other symmetric bipyrazoles is achieved via the palladium-catalyzed homocoupling of a pyrazole boronic ester in the presence of air and water, enabling us to provide the first crystal structures and evidence of structural phase changes in the bipyrazolate-based metal-organic framework Co(bpz).

Interstratified 2D nanohybrids of chromium hydroxide-molybdenum disulfide with improved electrode functionality are synthesized by the self-assembly of anionic monolayered MoS2 nanosheets with cationic chromium hydroxide nanoclusters. The intercalative hybridization of MoS2 with chromium hydroxide nanoclusters leads to a significant increase of basal spacing as well as to the formation of an open porous stacking structure. This is the first example of metal hydroxide nanocluster-pillared transition metal dichalcogenide (TMD) hybrid materials. According to extended X-ray absorption fine structure analysis, open tetrameric chromium hydroxide nanoclusters are stabilized in-between metallic 1T'-MoS2 monolayers. In comparison with the pristine MoS2 material, the chromium hydroxide-pillared molybdenum disulfide nanohybrids show remarkably improved charge storage capacity with excellent rate performance for lithium ion batteries, highlighting the beneficial effect of pillaring with metal hydroxides on the electrode performance of MoS2. The improvement of electrode functionality upon hybridization is attributable to the increase of basal spacing, the stabilization of metallic 1T'-MoS2 content, the improvement of charge transfer kinetics, and the stabilization of the open porous structure upon electrochemical cycling. The present study clearly demonstrates that an electrostatically-driven self-assembly between exfoliated TMD nanosheets and cationic inorganic nanoclusters can provide an effective way of synthesizing heterostructured hybrid electrode materials with improved performance.

Hexagonal and wormhole-type mesoporous geopolymers were developed by controlling the concentration of a structure directing agent (cetrimonium bromide, CTAB) with fixed ratios of Si/Al, KOH/(Si + Al), and H2O/(Si + Al), and their detailed porous structures were confirmed by TEM, N2 adsorption–desorption and X-ray diffraction measurements. The as-prepared geopolymers were then used as templates to replicate porous carbons with various structures and porosities for CO2 adsorption. To understand the correlation between the CO2 adsorptivity and porous structures, we tuned the porosity of the geopolymer-templated carbons by modifying the structures of the geopolymers. The porous carbons obtained from the hexagonal-type porous geopolymers were found to be composed of the aggregates of carbon nanowires exhibiting large particles, while those obtained from the wormhole-like porous geopolymers were determined to be wormhole type as well, as evidenced by TEM and X-ray diffraction studies. According to the CO2 adsorption isotherms of the porous carbons, the aggregates of carbon nanowires exhibited the highest CO2 adsorptivity due to their highest microporosity and largest specific surface area.

Theranostics that combines both diagnosis and therapy into a single platform has recently emerged as a promising biomedical approach for cancer treatment; however, the development of efficient theranostic agents with excellent optical properties remains a challenge. Here, we report novel mitochondria-targeting BODIPY photosensitizers (R-BODs) that possess considerable singlet oxygen generation capabilities and good fluorescence properties for imaging-guided photodynamic therapy (PDT). The incorporation of sulfur atoms into the π-conjugated skeleton of BODIPY along with the introduction of different functional groups at the meso-position of the BODIPY core is essential for tuning the photophysical and photosensitizing properties. Notably, the MeOPh-substituted thiophene-fused BODIPY (MeO-BOD, R = p-methoxyphenyl) displayed the highest singlet oxygen generation capability (ΦΔ ≈ 0.85 in air-saturated acetonitrile) and a moderate fluorescence quantum yield (Φf = 17.11). Furthermore, MeO-BOD showed good biocompatibility, low dark toxicity and superior fluorescence imaging properties in living cells. More importantly, the PDT efficacy of mitochondria-specific anchoring of MeO-BOD was remarkably amplified with an extremely low half-maximal inhibitory concentration (IC50) value of 95 nM. We believe that the incorporation of an electron-donating group at the meso-position of the thiophene-fused BODIPY platform may be an effective approach for developing theranostic agents for precision cancer therapy.