Martin Mkandawire

Marine biofouling presents a significant challenge, leading to the development of various antibiofouling solutions. While effective, traditional methods pose environmental risks due to toxic substances leaching into marine ecosystems. As a result, research is increasingly shifting towards focusing on sustainable alternatives. This review examined more than 100 studies on marine antibiofouling technologies, highlighting innovative approaches that minimize environmental impact. Key chemical deterrents include non-toxic biocides and various surface properties, while physical deterrents like altered surface topography and photocatalysts show promise. However, many eco-friendly solutions still depend on harmful substances. Future research should integrate multiple antifouling mechanisms and refine definitions of sustainability to assess life-cycle impacts. Collaboration among scientists, industry, and regulators is essential to foster innovation and adopt sustainable technologies for preserving marine ecosystems.

Galvanic interactions present alternative strategies to achieve a more efficient Cu dissolution from CuFeS₂. The present work studied the interaction between chalcopyrite–magnetite (CuFeS₂-Fe₃O₄) in acidified ferric sulphate Fe₂(SO₄)₃-H₂SO₄ at a solution pH of 1.8 and a temperature of 25 or 50 °C. The addition of Fe₃O₄ to CuFeS₂ forms a galvanic couple, which positively impacts the dissolution of Cu. The results showed that the presence of Fe₃O₄ led to high and fast Cu dissolution rates and decreased significantly the activation energy, from 83 to 57 kJ/mol. In addition to that, the solid residues revealed that CuFeS₂ dissolution produced intermediate Cu-S-rich phases: CuS, Cu₂S and Cu₅FeS₄, which appeared to envelop CuFeS₂, had no observable intermediate phase while in the presence of Fe₃O₄. The results showed that 94% of Cu could be recovered after 5 h of leaching at 50 °C at a Fe₃O₄/CuFeS₂ ratio of 4:1 and a 460 mV Ag/AgCl solution potential. The findings of this study present an option for efficient Cu dissolution from CuFeS₂ in ferric sulphate at atmospheric pressure.

Phthalates (PAEs) are a group of synthetic esters of phthalic acid compounds mostly used as plasticizers in plastic materials but are widely applied in most industries and products. As plasticizers in plastic materials, they are not chemically bound to the polymeric matrix and easily leach out. Logically, PAEs should be prevalent in the environment, but their prevalence, transport, fate, and effects have been largely unknown until recently. This has been attributed, inter alia, to a lack of standardized analytical procedures for identifying them in complex matrices. Nevertheless, current advancements in analytical techniques facilitate the understanding of PAEs in the environment. It is now known that they can potentially impact ecological and human health adversely, leading to their categorization as endocrine-disrupting chemicals, carcinogenic, and liver- and kidney-failure-causing agents, which has landed them among contaminants of emerging concern (CECs). Thus, this review article reports and discusses the developments and advancements in PAEs’ standard analytical methods, facilitating their emergence from obscurity. It further explores the opportunities, challenges, and limits of their advancements.

A growing quest for supercapacitors capable of quickly transferring energy has led to investigations focusing on developing electrode materials that incorporate noble metals due to their superior electrical conductivity. Here, we report the synthesis and charge storage performance of mesoporous silver molybdate electrodes of cubic β-Ag₂MoO₄ morphology and potatoes-like nanostructures. The electrochemical performance of the mesoporous β-Ag₂MoO₄ electrode has a battery-type behaviour with the transfer of two electrons (Ag⁰ ↔ Ag²⁺) during the redox reaction in 2 M KOH aqueous solution within a potential range of −0.45 to 0.35 V. In addition, the electrodes demonstrate quasi-conversion reaction during the discharge, which is due to the oxidation of unoxidized Ag⁰. Furthermore, the electrodes exhibit a maximum specific capacity of 2610 C g⁻¹ at 1 A g⁻¹ and significant retention of 82% upon 5000 continuous galvanostatic charge/discharge (GCD) cycles. A battery-type asymmetric supercapacitor cell (BASC) was designed using β-Ag₂MoO₄ as the positive electrode, activated carbon as the negative electrode, and polyurethane foam/KOH as the separator-cum-charge reservoir. The fabricated BASCs yielded maximum specific energy of 54 W h kg⁻¹ at a specific power of 194 W kg⁻¹. These appreciable electrochemical features suggest that β-Ag₂MoO₄ can be a viable material for developing supercapacitor electrodes.

The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS₂ phase dissolution produced intermediate Cu rich phases: CuS, Cu₂S and Cu₅FeS₄, which appeared to envelop CuFeS₂. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS₂ phase solid-state dissolution process was further discussed. Free Fe₃⁺ and its complexes (Fe(HSO₄)₂⁺, Fe(SO₄)^2– and FeSO₄⁺ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO₄)²⁺, Fe(SO₄)^2– and FeSO₄⁺, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe³⁺ and its complex (Fe(HSO₄)²⁺, while Fe(SO₄)^2– was the main species for the second Cu dissolution stage characterised by a slow rate.

Binary transition metal oxides, such as iron vanadate (FeVO₄), possess unleashed potential to be the best electrode material for supercapacitor, owing to their high capacitance, stability and conductivity. This present work reports investigations on the influence of a surfactant, polyethylene glycol (PEG 4000), on the structure, morphology and electrochemical behaviour of FeVO₄ nanoparticles. The P4-FeVO₄ exhibited specific capacitance of 428.0 Fg⁻¹ at a current density of 2.0 Ag⁻¹, and arguably better performance and cyclic stability than FeVO₄ synthesised without PEG 4000. Thus, PEG 4000 significantly influenced the morphological and electrochemical performance of the FeVO₄. Furthermore, the assembled P4-FeVO₄ based symmetric capacitor device had a specific capacitance of 101.0 Fg⁻¹ with an energy density of 14.1 Whkg⁻¹. This improved electrochemical performance of the P4-FeVO₄ based devices is attributed to the physicochemical properties of P4-FeVO₄ nanoparticles, mediated by the PEG 4000.