In this study, a variety of ZnO-based heterojunctions with disparate wt.% doping of WO₃ and BiOI have been prepared for the photodestruction of methyl orange (MO) dye in aqueous solution. The composites were analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, optical studies, and nitrogen adsorption-desorption isotherms. The SEM images revealed non-uniform surfaces of the ZnO–BiOI based composites while mostly nodular morphology was observed for all three samples of ZnO-WO₃. As the WO₃ loading increased, more clustering was detected. The analysed samples exhibited characteristic peaks representative of the triclinic phase of WO₃ and the hexagonal wurtzite structure of ZnO, while the diffractogram observed from the materials displayed distinct peaks corresponding to the crystalline phases of both BiOI and ZnO in their pure forms. Further evidence of the samples' characteristics includes the presence of distinct crystalline patterns without any impurity peaks, a red shift in the absorption spectra of the heterostructure, the detection of only the reference elements, and mostly Type IV isotherm adsorption. This study identified the ZnO-[10%]BiOI and ZnO-[10%]WO₃ heterojunctions as the best performing photocatalysts, as MO was completely destroyed in 120 and 90 min, respectively. Thus, confirming 10% wt. as the optimal doping concentration for the best photo-activity in this study. The impact of varying process parameters demonstrates that at an elevated photocatalyst mass of 40 mg, both heterojunctions effectively degraded MO. The photodegradation efficiency of MO was more pronounced in strong acidic conditions (pH 2) when compared to high alkaline conditions (pH 11) for the ZnO-[10%]BiOI heterostructure. However, a decrease in performance was observed for both strong acidic and high alkaline pH values when the ZnO-[10%]WO₃ heterostructure was applied. The kinetic analysis of the photodegradation study reveals that all the photodegradation experiments can be represented by the pseudo-first-order kinetic model. The findings from this investigation propose that the ZnO-[10%]BiOI heterojunction photocatalyst holds significant potential for the effective treatment of dye-contaminated wastewater.

This work provides a comprehensive overview of advanced characterisation techniques to unravel the molecular intricacies of catalytic processes. It begins with an introduction to catalytic processes and emphasises the importance of innovations in characterisation techniques, including SEM, XRD, UV-Vis, FTIR, RAMAN, XPS, NMR, TEM, AFM and the combined application of these techniques for improved catalytic investigation. The review of the development of catalytic processes provides a historical overview of progress and examines paradigm shifts in catalytic mechanisms and catalyst categories. Conventional microscopic and spectroscopic tools are revisited, highlighting the improvements in these techniques that provide insight into catalytic structures through surface analysis. Significant advances, including the application of computational techniques, in the study of catalysts are also discussed, focusing on state-of-the-art techniques that provide unprecedented detail on catalyst properties, mechanisms and processes. Comparative evaluations highlight the advantages and limitations of these techniques. The study concludes by identifying and overcoming challenges, anticipating prospects and emphasising the constant quest for innovation in understanding catalysts. By integrating developments in microscopic and spectroscopic methods, the study provides a comprehensive insight into how these tools improve the precision and depth of catalyst characterisation, driving innovation and future directions in catalysis research.

There are currently no studies on the synthesis and fabrication of ZnO-BiOI and ZnO-WO ₃ heterojunctions for the photocatalytic destruction of 2-chlorobiphenyl.

This study involved the synthesis, characterization, and application of various photocatalysts and heterojunctions using zinc oxide (ZnO), tungsten trioxide (WO₃), and bismuth oxyiodide (BiOI) for the photo-abatement of 2-chlorobiphenyl (2CBP). Scanning electron microscopy revealed a variety of morphologies for all composites, while energy-dispersive X-ray spectroscopy only identified reference elements and X-ray diffraction patterns displayed crystalline patterns with no impurity peaks. The absorbance of the heterostructures exhibited slight red shifts as WO₃ and BiOI were etched into ZnO. Except for ZnO-[10%]WO₃, the band gaps of all composites decreased/narrowed as the doping of WO₃ and BiOI into ZnO increased. Nitrogen sorption isotherms revealed that almost all the prepared materials had a Type IV isotherm, and the heterostructures showed higher surface area measurements compared to the undoped composites. The ZnO-[10%]BiOI heterojunction, which displayed the best photoactivity, was further investigated to analyze the influence of some operating conditions. Results revealed that the initial pollutant concentration influenced the degree of photodegradation, which decreased with increased initial 2CBP concentration. The optimum photocatalytic performance was detected at neutral pH. The pseudo-first order kinetic model showed that doubling the heterojunction’s weight increased the rate constant from 0.0054 to 0.0089 min⁻¹, while increasing the pH to 11.3 resulted in an 18-fold reduction. Overall, the study demonstrated the potential application of ZnO-[10%]BiOI heterostructure as a highly effective photocatalyst for recalcitrant contaminants in water.

Over the past decade, the term "circular economy" has become increasingly important, particularly in the areas of sustainability, resource management, and productivity. This concept is now being actively considered and implemented by national, public, and private organisations worldwide. As concerns about the impacts of climate change increase, so do discussions about mitigating its consequences. An important aspect of this discourse is the shift from fossil fuels to renewable energy sources. Recognising the unacceptable phenomenon of climate change, particularly global warming, the South African government has committed to reducing greenhouse gas (GHG) emissions and promoting green mobility through the Just Energy Transition Investment Plan (JET-IP). This study aims to provide a critical review of South Africa’s JET-IP, evaluating the feasibility of the proposed decarbonization of the energy sector by identifying key constraints and opportunities for a successful transition. The approach involved a critical review of South Africa’s Just Energy Transition (JET) policy documents, government documents, and related publications, focusing on the 5-year transition plan. The emphasis is on the status and opportunities of the five-year (2023–2027) JET-IP in South Africa, considering the potential of renewable energy sources in the country. The study reveals that South Africa’s 5-year JET-IP faces two interconnected challenges that hinder its feasibility and smooth implementation: the slow deployment of renewable energy sources and obstacles to ensuring reliable and affordable energy. These challenges stem from resistance to decommissioning coal-fired power generation and austerity-driven utility policies. The study offers perspectives and proposes strategic pathways to accelerate the integration of renewable energy technologies into the country’s current energy mix. The findings provide insights into South Africa’s Just Energy Transition, applicable to fossil fuel-dependent countries, particularly in the coal-reliant Global South. Graphical abstract

Mining industries have long relied on cyanidation as the primary method for gold extraction, but this process generates thiocyanates as a problematic byproduct, posing challenges for wastewater treatment and recycling. The stability of thiocyanates makes their reduction or elimination in mining wastewater difficult. In this study, a p-n heterojunction of ZnO and BiOI was created and evaluated for its ability to photodegrade thiocyanate ions under simulated solar conditions. Various analytical techniques revealed a highly porous structure with a sponge-like morphology and agglomeration in the synthesized heterojunction. The compound exhibited crystalline patterns without impurity peaks, a slight red shift in absorbance, and Type IV isotherm adsorption. The synthesized heterostructure achieved the complete destruction of thiocyanate ions in less than 30 min. The investigation of different process parameters indicated that the destruction of the contaminant by the heterostructure was influenced by the initial thiocyanate concentration, which decreased as the thiocyanate concentration increased. The peak photodestruction reaction was observed at pH 7. By applying a pseudo-first-order kinetic model, it was found that increasing the catalyst mass to 15 mg raised the rate constant from 0.188 to 0.420 min⁻¹, while increasing the pH to 10 led to a 3.5-fold reduction. The strong correlation between the observed data and the predicted values of the pseudo-first-order kinetic model was indicated by the observed (R²) values. The findings of this study hold potential significance for mining industries, as it offers a potential solution for eliminating cyanide and thiocyanates from mining wastewater. The elimination of thiocyanate generation in the cyanidation process is crucial for mining companies, making this study valuable for the industry.