Nurrulhidayah Salamun

Synergistic interactions of Cu and N on surface altered amorphous TiO2 nanoparticles for enhanced photocatalytic oxidative desulfurization of dibenzothiophene

Amorphous TiO2 (AT) nanoparticles were prepared by a simple sol–gel method and subsequent incorporation with copper (5–20 wt%) via an electrochemical method in the presence of a supporting electrolyte, tetraethylammonium perchlorate (TEAP), was used to synthesize CuO/TiO2 (CAT) catalysts. The physicochemical properties of the catalysts were studied by XRD, N2 adsorption–desorption, TEM, FTIR, XPS, ESR and UV-Vis DRS. Photocatalytic testing on the oxidative desulfurization of dibenzothiophene (DBT) under UV and visible light irradiation demonstrated that the CAT catalysts were active under both conditions. It was found that Ti3+ surface defects (TSD), oxygen vacancies (Vo), CuO, Ti–O–N/O–Ti–N and Ti–O–Cu bonds played an important role in photooxidation. The TSD, Vo, CuO, N 1s and Cu 2p states in the CAT catalysts acted as electron trappers to hinder electron–hole recombination. In addition, these TSD, Vo, N 1s and Cu 2p species also contributed to the lowering of the CAT band gap, which enabled photooxidation to be carried out in the visible light region. The photooxidation followed a pseudo-first order Langmuir–Hinshelwood model with adsorption being the controlling step.

Acid-vacuo heat treated low cost banana stems fiber for efficient biosorption of Hg(II)

The potential of banana stem fiber (BSF) as a low cost biosorbent for Hg(II) removal was studied. HCl treatment increased the cellulose accessibility which led to an enhanced interaction of Hg(II) and BSF. Activation of BSF-HCl in vacuo at 373 K increased the maximum biosorption capacity from 28 to 372 mg g−1 and altered the activation energy from 3.5 to 76.9 kJ mol−1 showing an increase in Hg(II) chemisorption. FTIR and ESR results confirmed the large amount of structural defects on the activated BSF-HCl which led to the increase in Hg(II) uptake. Batch biosorption models showed that the kinetics follow pseudo-second-order and the equilibrium uptake fitted to all three-parameter models showing the Hg(II) biosorption behaves as a Langmuir isotherm. The non-linear regression method exhibited higher coefficient of determination values for isotherm and kinetic analyses compared to the linear method. The thermodynamic functions indicated that the nature of Hg(II) biosorption is an exothermic and non-spontaneous process.

Surface modification of banana stem fibers via radiation induced grafting of poly(methacrylic acid) as an effective cation exchanger for Hg(II)

A low cost adsorbent, banana stem fibers (BSFs), was used for modification by grafting with methacrylic acid via three free radical generation methods. The presence of poly(methacrylic acid) on the adsorbent surface was verified by FTIR, ESR and TG analyses. BSFs grafted via β-radiation (BSF-β) were proven to have a higher grafting yield which led to a higher Hg(II) adsorption capacity. A slight decrease in the equilibrium pH after the adsorption process was probably due to BSF-β acting as an acid-form ion-exchanger. The adsorption equilibrium uptake fitted well with the Freundlich isotherm model implying that Hg(II) adsorption occurred heterogeneously on the adsorption sites. The kinetics of adsorption follows a pseudo-first order model with an activation energy of 13.7 kJ mol−1 indicating that the adsorption undergoes an ion-exchange process. Thermodynamic studies illustrated that that the Hg(II) adsorption process was endothermic and non-spontaneous. Spent BSF-β was effectively regenerated with 0.1 M HCl and could be reused without any significance efficiency loss over at least six cycles of adsorption. The present investigation shows that BSF-β is a promising adsorbent for the removal and recovery of Hg(II) ions from aqueous solutions.