Biomass-promoting routes for the synthesis of activated carbon (AC) have recently received considerable attention due to the advantages of this method: it is simple, cost-effective, and ecofriendly. This method is also an alternative way to avoid the unsafe practice of waste incineration. We describe the preparation of activated carbon from palm kernel shell (PKS) - an abundant biomass that is available in Africa and Asia. We investigated the effect of process variables such as impregnation ratio (ratio of H3PO4 to PKS) and carbonisation temperature (500-700 °C) on yield, microstructure, morphology, pore structure, and adsorption properties to optimise these parameters. Nitrogen adsorption isotherm analysis indicated that the AC was predominantly microporous in nature. Under optimal conditions, an AC with the highest surface area of 1560 m²/g was obtained. The aqueous adsorption test showed that the AC had significant removal capacity for methylene blue and iodine. The higher iodine value is consistent with the structural properties of the adsorbent, while the lower methylene blue value is consistent with the limited mesopore width. Considering the chemical and surface properties and adsorption properties of the AC produced, PKS has been shown to be an excellent precursor material for AC, thus solving the disposal problems associated with this biomass. SIGNIFICANCE: •AC significantly promotes adsorption and offers a low-cost and cleaner production method. •PKS could serve as a dependable precursor for the synthesis of porous AC. •This study provides useful information on how H3PO4-impregnated PKS influences the porosity of the resulting AC. •Differences in porosity, yield, and morphology and Brunauer-Emmet-Teller surface area are achievable using AC from PKS

Resumo As competências metacognitivas desempenham um papel importante na resolução de problemas matemáticos. No entanto, existe falta de estudos empíricos sobre o papel das competências metacognitivas na resolução de problemas matemáticos, em particular os não rotineiros. Portanto, este estudo foi realizado para identificar competências metacognitivas dos alunos e o impacto de tais competências na resolução de problemas matemáticos não-rotineiros. Usando um método quantitativo, um total de 304 estudantes no distrito de Johor Bahru foram envolvidos no estudo. Questionário de Monitorização Autónomo (SMQ) e teste de matemática foram utilizados na recolha de dados. Os dados obtidos foram analisados por meio de estatística descritiva e inferencial, como a frequência, porcentagem, média, o teste de Mann-Whitney e Kruskal-Wallis H. Os resultados mostraram que o nível de desempenho dos alunos na resolução de problemas matemáticos não-rotineiros era muito baixa. Conclui-se uma diferença significativa nas competências metacognitivas entre estudantes com diferentes níveis de desempenho na resolução de problemas matemáticos não rotineiros. Concluiu-se que as competências metacognitivas devem ser enfatizadas no processo de resolução de problemas matemáticos não rotineiros.

Abstract Metacognitive skills play an important role in solving mathematical problems. However, there is a lack of empirical studies on the role of metacognitive skills in solving mathematical problems, particularly non-routine ones. Therefore, this study was undertaken to identify students' metacognitive skills and the impact of such skills on non-routine mathematical problem solving. By using a quantitative method, a total of 304 students in Johor Bahru district were involved in the study. A Self-Monitoring Questionnaire (SMQ) and a mathematical test were used in data collection. Data were analysed using descriptive and inferential statistics such as frequency, percentage, mean, the Mann-Whitney U test, and the Kruskal-Wallis H test. Results showed that the level of the students' performance in solving non-routine mathematical problems was very low. There was also a significant difference in the metacognitive skills among students with different performance levels in solving non-routine mathematical problems, and we concluded that these metacognitive skills should be emphasised in this process.

O presente artigo relata a degradação UV-assistida de 1,4-benzoquinona em suspensões ZnO. As variáveis estudadas incluem a concentração de 1,4-benzoquinona, fotocatalisador, pH e carbono orgânico total. A concentração de 1,4-benzoquinona e o carbono orgânico residual foram medidos usando espectrofotômetro UV-Visível e analisador TOC, respectivamente. Os resultados mostraram que a fotodegradação da 1,4-benzoquinona foi independente do pH. A fotoatividade do ZnO foi máxima na concentração de 1,0 g L-1 e em níveis de 100 mg L-1 de 1,4-benzoquinona. Na faixa de pH 4-10 mais de 80% de 1,4-benzoquinona pode ser removida. ZnO demonstrou capacidade de reutilização no processo.

The present paper reports the UV-assisted degradation of 1,4-benzoquinone in ZnO suspensions. The variables studied include the concentration of 1,4-benzoquinone, photocatalyst, pH and the total organic carbon. The concentration of 1,4-benzoquinone and residue organic carbon were measured using UV-Visible spectrophotometer and TOC analyzer, respectively. The results showed that 1,4-benzoquinone photodegradation was independent of pH. The photoactivity of ZnO was maximum at 1.0 g L-1 concentration and at 100 mg L-1 1,4-benzoquinone levels. Within pH 4-10 more than 80% of 1,4-benzoquinone can be removed. ZnO has demonstrated reusability in the process.