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There are on-going investigations on the utilization of pineapple leaf fibre (PALF) as a cheap, safe, and eco-friendly natural fibre. The present work aimed to improve PALF preparation using ultrasonication, investigate the adsorption kinetic and thermodynamic aspects of PALF dyed with berberine dye, and to assess their associated molecular interactions. It was found that concomitant PALF exposure to NaOH solution (5% w/v) plus ultrasonication for 20 min successfully removed non-cellulosic substances from the fibre surface in a very much shorter time compared with the traditional non-ultrasound assisted method (24 h). An adsorption isotherm study of dyeing, the treated fibre with the natural yellow dye berberine revealed a strong adsorption dependence on the pH of the berberine solution with optimal uptake occurring at pH 9–10. A deeper assessment of the mode of dye binding was undertaken by DFT − based calculations on a model cellulose unit and berberine. It revealed that the interaction between berberine and cellulose (PALF) at pH 9.00 was likely to be substantially stronger than at lower pH. From the adsorption kinetic results, a higher affinity and more dye uptake were observed before equilibrium was reached. The adsorption isotherm data could be represented by the Langmuir isotherm (R2 > 0.99). The enthalpy change (ΔH°) and entropy change (ΔS°) values of dyeing were found to be −17.0 kJ mol−1 and −19.4 J mol−1 K−1 respectively, which pointed to the dye adsorption being an exothermic process. The negative standard affinity (Δµo) values at the different temperatures of 30, 60, and 80 °C were −11.2, −10.6, and −10.2 kJ mol−1, respectively. It affirmed the dye adsorption process as a spontaneous one. Higher temperatures resulted in a lower affinity and reduced dye uptake compatible with the process being exothermic. Berberine is a potentially useful natural dye for PALF without the need for additives. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) leads to corrosion in transport lines and poisoning of many catalysts. Meanwhile, H2S is an inexhaustible potential source of hydrogen, which is a very valuable chemical reagent and an environmentally friendly energy product. Therefore, removal of H2S and producing hydrogen gas using potential catalysts has been intensively studied, according to the equation: H2S(g) + CO(g) → COS(g) + H2(g). In this study, hydrogen sulfide (H2S) decomposition in the presence of CO over transition metal-doped ZSM-12 clusters (TM-ZSM-12) has been investigated based on DFT calculations at the B3LYP-D3/6-31G(d,p) level. The calculation results reveal that the proposed reaction mechanism is controlled by 4 key steps, (i) hydrogen dissociation (Ea1 = +0.04 eV for the 1st hydrogen and Ea2 = +0.22 eV for the 2nd hydrogen), (ii) COS desorption (the rate-determining step of this H2S removal process, Edes = +1.18 eV), (iii) hydrogen diffusion to the transition metal with an energy barrier (Ea3) of +0.62 eV, and (iv) the H2 formation step (Ea4 = +0.94 eV). Our results indicate that in the presence of CO, the Cu–ZSM-12 cluster has a potential application as a highly active catalyst for H2S removal together with hydrogen production. [ABSTRACT FROM AUTHOR]

Conversion of carbon dioxide (CO2) to more valuable chemicals is nowadays receiving increasing attention from an environmental and industrial point of view. Herein, we computationally investigated CO2 hydrogenation to formic acid on Lewis acid zeolites by means of density functional theory (DFT) with the M06-L functional. The reaction proceeds in two steps, hydrogenation of CO2 to form the formate intermediate and hydrogen-abstraction to form formic acid. A defect zeolite seems to be favored over a perfect one, leading to its low rate determining step barrier of 5.2 kcal mol−1. We also considered the effect of the zeolite frameworks and found that the catalytic activities are in the order Sn-ZSM-5 ＞ Sn-BEA ＞ Sn-FAU. Finally, we performed catalytic activity screenings of tetravalent metals (Ge, Zr and Hf) substituted into the defect Sn-ZSM-5 zeolite. The order Hf ＞ Zr ＞ Sn ＞ Ge was found based on the rate determining step activation energy. The difference in activation energy can be explained by the difference in charge transfer from the catalytic site to the reacting molecules. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) leads to corrosion in transport lines and poisoning of many catalysts. Meanwhile, H 2 S is an inexhaustible potential source of hydrogen, which is a very valuable chemical reagent and an environmentally friendly energy product. Therefore, removal of H 2 S and producing hydrogen gas using potential catalysts has been intensively studied, according to the equation: H 2 S(g) + CO(g) → COS(g) + H 2 (g). In this study, hydrogen sulfide (H 2 S) decomposition in the presence of CO over transition metal-doped ZSM-12 clusters (TM-ZSM-12) has been investigated based on DFT calculations at the B3LYP-D3/6-31G(d,p) level. The calculation results reveal that the proposed reaction mechanism is controlled by 4 key steps, (i) hydrogen dissociation (E a1 = +0.04 eV for the 1st hydrogen and E a2 = +0.22 eV for the 2nd hydrogen), (ii) COS desorption (the rate-determining step of this H 2 S removal process, E des = +1.18 eV), (iii) hydrogen diffusion to the transition metal with an energy barrier (E a3 ) of +0.62 eV, and (iv) the H 2 formation step (E a4 = +0.94 eV). Our results indicate that in the presence of CO, the Cu-ZSM-12 cluster has a potential application as a highly active catalyst for H 2 S removal together with hydrogen production.

Conversion of carbon dioxide (CO2) to more valuable chemicals is nowadays receiving increasing attention from an environmental and industrial point of view. Herein, we computationally investigated CO2 hydrogenation to formic acid on Lewis acid zeolites by means of density functional theory (DFT) with the M06-L functional. The reaction proceeds in two steps, hydrogenation of CO2 to form the formate intermediate and hydrogen-abstraction to form formic acid. A defect zeolite seems to be favored over a perfect one, leading to its low rate determining step barrier of 5.2 kcal mol-1. We also considered the effect of the zeolite frameworks and found that the catalytic activities are in the order Sn-ZSM-5 > Sn-BEA > Sn-FAU. Finally, we performed catalytic activity screenings of tetravalent metals (Ge, Zr and Hf) substituted into the defect Sn-ZSM-5 zeolite. The order Hf > Zr > Sn > Ge was found based on the rate determining step activation energy. The difference in activation energy can be explained by the difference in charge transfer from the catalytic site to the reacting molecules.