Mineralization of palm oil mill effluent by advanced oxidation processes: A review on current trends and the way forward

Palm oil mill effluent (POME) is regarded as deleterious to the environment, primarily owing to the substantial volume of waste it produces during palm oil extraction. In terms of contaminant composition, POME surpasses the pollutant content typically found in standard municipal sewage, therefore releasing it without treatment into water bodies would do irreparable damage to the environment. Main palm oil mills are normally located in the proximity of natural rivers in order to take advantage of the cheap and abundant water source. The same rivers are also used as a water source for many villages situated along the river banks. As such, it is imperative to degrade POME before its disposal into the water bodies for obvious reasons. The treatment methods used so far include the biological processes such as open ponding/land application, which consist of aerobic as well as anaerobic ponds, physicochemical treatment including membrane technology, adsorption and coagulation are successful for the mitigation of contaminants. As the above methods require large working area and it takes more time for contaminant degradation, and in consideration of the strict environmental policies as well as palm oil being the most sort of vegetable oil in several countries, numerous researchers have concentrated on the emerging technologies such as advanced oxidation processes (AOPs) to remediate POME. Methods such as the photocatalysis, Fenton process, sonocatalysis, sonophotocatalysis, ozonation have attained special importance for the degradation of POME because of their efficiency in complete mineralization of organic pollutants in situ. This review outlines the AOP technologies currently available for the mineralization of POME with importance given to sonophotocatalysis and ozonation as these treatment process removes the need to transfer the pollutant while possibly degrading the organic matter sufficiently to be used in other industry like fertilizer manufacturing.

The use of food additives as green and environmental-friendly anti-corrosion inhibitors for protection of metals and alloys: a review

Corrosion inhibitors have offered new opportunities to bring positive impacts on our society, especially when it has helped in protecting metals against corrosion in an aqueous solution. Unfortunately, the commonly known corrosion inhibitors used to protect metals or alloys against corrosion are invariably related to one or more drawbacks such as the employment of hazardous anti-corrosion agents, leakage of anti-corrosion agents in aqueous solution, and high solubility of anti-corrosion agents in water. Over the years, using food additives as anti-corrosion agents have drawn interest as it offers biocompatibility, less toxic, and promising applications. In general, food additives are considered safe for human consumption worldwide, and it was rigorously tested and approved by the US Food and Drug Administration. Nowadays, researchers are more interested in innovating and using green, less toxic, and economical corrosion inhibitors in metal and alloy protection. As such, we have reviewed the use of food additives to protect metals and alloys against corrosion. The current review is significant and differs from the previous review articles made on corrosion inhibitors, in which the new role of food additives is highlighted as green and environmental-friendly substances in the protection of metals and alloys against corrosion. It is anticipated that the next generation will be utilizing non-toxic and sustainable anti-corrosion agents, in which food additives might be the potential to fulfill the green chemistry goals.

Valorization of discarded face mask for bioactive compound synthesis and photodegradation of dye

To keep COVID-19 at bay, most countries have mandated the use of face masks in public places and imposed heavy penalties for those who fail to do so. This has inadvertently created a huge demand for disposable face masks and worsened the problem of littering, where a large number of used masks are constantly discarded into the environment. As such, an efficient and innovative waste management strategy for the discarded face mask is urgently needed. This study presents the transformation of discarded face mask into catalyst termed 'mask waste ash catalyst (MWAC)' to synthesise bisindolylmethanes (BIMs), alkaloids that possess antibacterial, antioxidant and antiviral properties. Using commercially available aldehydes and indole, an excellent yield of reaction (62-94%) was achieved using the MWAC in the presence of water as the sole solvent. On the other hand, the FT-IR spectrum of MWAC showed the absorption bands at 2337 cm^-1, 1415 cm^-1 and 871 cm^-1, which correspond to the signals of calcium oxide. It is then proposed that the calcium oxides mainly present in MWAC can protonate oxygen atoms in the carbonyl molecule of the aldehyde group, thus facilitating the nucleophile attack by indole which consequently improved the product yield. Moreover, the MWAC is also observed to facilitate the photodegradation of methylene blue with an efficiency of up to 94.55%. Our results showed the potential applications of the MWAC derived from discarded face masks as a sustainable catalyst for bioactive compound synthesis and photodegradation of dye compounds.

Volatile Organic Compounds of Bryophytes from Peninsular Malaysia and Their Roles in Bryophytes

Volatile emissions from 22 bryophyte species from Peninsular Malaysia were collected using a dynamic headspace technique and analyzed by gas chromatography-mass spectrometry (GC-MS). Thirty organic compounds (VOCs) from eight different groups were detected in bryophytes from the montane forest in Cameron Highlands and the lowland dipterocarp forest in Lata Belatan. The headspace of bryophytes in Cameron Highlands was dominated by tetradecane, 2-ethyl-1-hexanol, decanal, pentanoic acid, 2,2,4-trimethyl-3-carboxyisopropyl, isobutyl ester, D-limonene and naphthalene. On the contrary, in the bryophyte headspace of Lata Belatan, naphthalene and tetradecane were dominant compounds. The elevational pattern detected in VOC composition of bryophytes appears to be an evolutionary feature at the family level that needs verification at other sites. The results also confirmed that the VOC composition of bryophytes is species-specific. The roles of VOCs in bryophytes are presented, including plant-plant communication and plant-insect interaction and as an additional taxonomic character in chemotaxonomy.

Allelopathic Potential of Cassava (Manihot esculenta L.) Extracts on Germination and Seedling Growth of Selected Weeds and Aerobic Rice

Weed infestation is a major problem in the aerobic rice system due to the lack of standing water that could prevent the growth of weeds. To reduce heavy reliance on herbicide, this research aims to determine the potential of cassava allelopathy for inhibition of weeds in aerobic rice. The allelopathic potential of cassava extracts on the germination and growth of tested weed species (Eleusine indica, Ageratum conyzoides, and Cyperus distans) and aerobic rice (Oryza sativa) was conducted in the laboratory. The results showed that increasing the aqueous extract concentrations of cassava extracts inhibited the germination and seedling growth of tested weeds, suggesting the allelopathic effects of cassava extracts are concentration dependent. The degree of phytotoxicity of different vegetative parts of cassava can be classified in order of decreasing inhibition as follows: leaf, stem, tuber, and tuber peel. Aqueous leaf extract of cassava at a concentration of 0.5% (w/v) provided complete inhibition on A. conyzoides, E. indica, and C. distansgermination whereas 25% to 100% inhibition on the shoot growth was recorded. By contrast, the shoot growth and germination of aerobic rice were not affected. These results suggest that the cassava leaf extracts contain water-soluble allelochemicals for inhibition on A. conyzoides, E. indica, and C. distans in aerobic rice.

Herbicidal properties of antihypertensive drugs: calcium channel blockers

Herbicide resistance is a worldwide problem in weed control. This prompts researchers to look for new modes of action to slow down the evolution of herbicide-resistant weeds. This research aims to determine the herbicidal action of thiazolo[3,2-a]pyrimidines derivatives, which are well known as antihypertensive drugs. The phytotoxic effects of ten compounds were investigated using leaf disc discoloration test and seed germination bioassay. At concentrations of 125 to 250 mg/L, the 5-(3-Fluoro-phenyl)-7-methyl-5H-thiazolo[3,2-a]pyrimidine-6-carboxylic acid ethyl ester (c) was highly active against Oldenlandia verticillata and Eleusine indica. At application rates of 1.25 to 2.5 kg ai/ha, formulated c demonstrated selective post-emergence and pre-emergence herbicidal activity against O. verticillata, E. indica and Cyperus iria. In the crop tolerance test, formulated c outperformed the commercial herbicide diuron, with aerobic Oryza sativa being the most tolerant, followed by Zea mays, and Brassica rapa. The addition of calcium chloride partially nullified compound c's inhibitory effects on weed shoot growth, indicating that it has potential as a calcium channel blocker. Compound c acted by triggering electrolyte leakage without affecting photosystem II. These findings imply that c could be explored further as a template for developing new herbicides with novel modes of action.

Green synthesis, characterization and applications of silver nanoparticle mediated by the aqueous extract of red onion peel

This manuscript describes the reuse of biowaste for the biosynthesis of silver nanoparticles (AgNPs) and their applications. In particular, we hypothesized that the phytochemicals in the onion peels could act as reductant for silver nanoparticles syntheses. AgNO₃ solution (1 mmol) was added dropwise to an aqueous solution of onion peel extract in 3:7 ratio. The reaction mixture was subjected to heating at 90 °C for about 30 min. During the synthesis of the AgNPs, the change of the colour of solution was observed. The AgNPs solution was centrifuged to obtain the two layers, which consists of clear solution and solid layers at 12000 rpm for 30 min. The precipitate was filtered and was re-dispersed in deionised water (25 mL). The solution was centrifuged again to obtain the purified AgNPs. Subsequently, this solution was freeze dried for 48 h to afford the powdered AgNPs. In this work, the structure of the AgNPs were synthesized in spherical shape, with an average size of 12.5 nm observed in the Transmission electron microscopy (TEM) analysis. For catalytic application, the synthesized AgNPs could be applied as green catalyst to promote Knoevenagel and Hantzsch reactions. In most cases, the desired products were obtained in satisfactory yields. In addition, the AgNPs were found to be recyclable for the subsequent reactions. After five successive runs, the average isolated yields for both transformations were recorded to be 91% (Knoevenagel condensation) and 94% (Hantzsch reaction), which indicated that the existing AgNPs could apply as green catalyst in the field of organic synthesis. Furthermore, the AgNPs also showed satisfactory result in antioxidant activity. The current results indicate that the AgNPs can act as alternative antioxidant agent and green catalyst in mediating organic transformations.

Gasification of refuse-derived fuel from municipal solid waste for energy production: a review

Dwindling fossil fuels and improper waste management are major challenges in the context of increasing population and industrialization, calling for new waste-to-energy sources. For instance, refuse-derived fuels can be produced from transformation of municipal solid waste, which is forecasted to reach 2.6 billion metric tonnes in 2030. Gasification is a thermal-induced chemical reaction that produces gaseous fuel such as hydrogen and syngas. Here, we review refuse-derived fuel gasification with focus on practices in various countries, recent progress in gasification, gasification modelling and economic analysis. We found that some countries that replace coal by refuse-derived fuel reduce CO₂ emission by 40%, and decrease the amount municipal solid waste being sent to landfill by more than 50%. The production cost of energy via refuse-derived fuel gasification is estimated at 0.05 USD/kWh. Co-gasification by using two feedstocks appears more beneficial over conventional gasification in terms of minimum tar formation and improved process efficiency.

Fluorinated 5- and 7-membered carbacycle motifs by reaction of difluorocarbene with acetylene ethers

The reaction of acetylene ethers with difluorocarbene (CF(2)), generated from the Ruppert-Prakash reagent, unexpectedly gave rise to co-produced fluorinated bicyclic [2.1.1]-hex-2-ene and cyclohepta-1,4-diene ring products.