Potential of low-cost TiO2-PVC composite in photoelectrocatalytic degradation of reactive orange 16 under visible light.

In recent years, previously reported studies revealed a high efficiency of pollutant degradation by coupling photocatalysis and electrochemical processes (PECs) using titanium dioxide (TiO2) photoelectrode rather than using photocatalysis or electrocatalysis alone. However, some of the TiO2 photoelectrodes that have been reported were not cost-effective. This is due to the use of expensive chemicals and certain expensive equipment in the fabrication process, other than involving complicated preparation steps. Therefore, this study is aimed at investigating the PEC performance and stability of low-cost TiO2-polyvinyl chloride (TiO2-PVC) composite photoelectrode for Reactive Orange 16 (RO16) degradation. The materials characterisation using the ATR-FTIR, XRD and UV-Vis DRS proved that TiO2 and TiO2-PVC were successfully synthesised. The micrograph obtained for the surface characterisation using the FESEM showed that the smooth surface of freshly prepared photoelectrodes turned slightly rough with tiny pits formation after five continuous PEC processes. Nevertheless, the photoelectrode retained its original shape in good condition for further PEC processes. By PEC process, the fabricated photoelectrode showed 99.4% and 51.1% of colour and total organic carbon (TOC) removal, respectively, at optimised PEC parameters (1.0 mol L-1 NaCl concentration, 10 V applied voltage, 120 min degradation time and initial pH 2). Moreover, the fabricated photoelectrode demonstrated sufficient reusability potential (~ 96.3%) after five cycles of PEC processes. In summary, a low-cost and stable composite photoelectrode with high efficiency in RO16 degradation was successfully fabricated and could be potentially applied for other emerging pollutants degradation via the PEC degradation technique.

Effect of metal doping (Me = Zn, Cu, Co, Mn) on the performance of bismuth ferrite as peroxymonosulfate activator for ciprofloxacin removal.

In this study, a facile hydrothermal method was employed to prepare Me-doped Bi2Fe4O9 (Me = Zn, Cu, Co, and Mn) as peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) degradation. The characteristics of the Me-doped bismuth ferrites were investigated using various characterization instruments including SEM, TEM, FTIR and porosimeter indicating that the Me-doped Bi2Fe4O9 with nanosheet-like square orthorhombic structure was successfully obtained. The catalytic activity of various Me-doped Bi2Fe4O9 was compared and the results indicated that the Cu-doped Bi2Fe4O9 at 0.08 wt.% (denoted as BFCuO-0.08) possessed the greatest catalytic activity (kapp = 0.085 min-1) over other Me-doped Bi2Fe4O9 under the same condition. The synergistic interaction between Cu, Fe and oxygen vacancies are the key factors which enhanced the performance of Me-doped Bi2Fe4O9. The effects of catalyst loading, PMS dosage, and pH on CIP degradation were also investigated indicating that the performance increased with increasing catalyst loading, PMS dosage, and pH. Meanwhile, the dominant reactive oxygen species was identified using the chemical scavengers with SO4•-, •OH, and 1O2 playing a major role in CIP degradation. The performance of BFCuO-0.08 deteriorated in real water matrix (tap water, river water and secondary effluent) due to the presence of various water matrix species. Nevertheless, the BFCuO-0.08 catalyst possessed remarkable stability and can be reused for at least four successive cycles with >70% of CIP degradation efficiency indicating that it is a promising catalyst for antibiotics removal.

Promotional effect of Ca doping on Bi2Fe4O9 as peroxymonosulfate activator for gatifloxacin removal.

A series of Ca-doped bismuth ferrite was prepared at various %w/w of Ca via a facile hydrothermal method to obtain Bi2XCa2(1-X)Fe4O9 (denoted as BFOCa-X, where X = 1, 0.95, 0.90, 0.80, 0.50). The BFOCa-X catalysts were characterized, and the results showed that they consist of pure phase BFO with nanosheet-like morphology. The as-prepared BFOCa-X catalysts were used as peroxymonosulfate (PMS) activator for gatifloxacin (GAT) removal. It was found that the catalytic activity decreased in the following order: BFOCa-0.8 (90.2% GAT removal efficiency in 45 min, kapp = 0.084 min-1)>BFOCa-0.95 > BFOCa-0.9 > BFOCa-0.5 > BFO indicating that BFOCa-0.8 has the optimized active sites for catalysis. The Ca dopant contributed to the increased oxygen vacancies and surface hydroxyl groups, promoting the catalytic PMS activation process. The kapp value increased gradually with increasing catalyst loading and PMS dosage while pH 9 presented the highest GAT removal rate. The GAT degradation rate was inhibited by PO43-, humic acid and NH4+ but promoted in the presence of Cl-, NO3- and HCO3-. It was also found that the GAT can undergo several degradation pathways in the catalytic PMS system, which eventually mineralized into innocuous compounds. The dominant reactive oxygen species (ROS) were identified using chemical scavengers, revealing that SO4•-, 1O2 and •OH contributed significantly to GAT degradation. Based on the XPS study, PMS was activated by the Fe2+/Fe3+ redox cycling and oxygen vacancies to produce SO4•-/•OH and 1O2, respectively. Overall, the BFOCa-0.8 also showed excellent reusability up to at least 4 cycles with low Bi and Fe leaching (<7 and 62 µg L-1, respectively), indicating that it has promising potential for application as PMS activator for antibiotics removal.

A Review on Recent Progression of Modifications on Titania Morphology and its Photocatalytic Performance.

Titanium dioxide (TiO2) has been broadly used as a photocatalyst because it has good stability and performance for degradation of pollutants. On the other hand, its efficiency as photocatalyst is limited since it can only be excited under UV-light radiation and has a rapid electron-hole recombination that occurs during the photodegradation. There are many studies focusing on adjusting the synthesis methods, addition of dopants and modifying the TiO2 structure to enhance its photocatalytic performance. Among them, synthesis of TiO2 as porous nanoparticles as one of the strategies in modifying the TiO2 structure has gained attention due to its benefits for better adsorption and accessibility of various pollutants onto the reactive site of catalyst, thus enhancing the photocatalytic performance. In this review, we recapitulated on modifications of synthesis methods for TiO2 and their effect on the structure along with the photocatalytic performance. Recent progress for TiO2 in terms of synthesis approaches, effect of dopants, modified structures, and applications are also briefly discussed in this review.

Electrochemical Degradation of Reactive Blue 21 and Synthetic Textile Effluent by Using Co47.5/C47.5-PVC5 Composite Electrode.

In this study, cobalt/graphite-polyvinyl chloride (Co47.5/C47.5-PVC5) composite electrode was fabricated by mechanical alloying technique. The fabricated electrode and graphite rod were used as anode and cathode, respectively, in the decolourisation of aqueous C. I. Reactive Blue 21 (RB21) and synthetic textile effluent, containing a mixture of azo and anthraquinone dyes. The fabricated electrode showed high efficiency in the decolorisation of aqueous RB21 (99.95%) and synthetic textile effluent. This is further confirmed by the high reduction percentage (>75%) of COD and BOD5 for both treated samples. The elemental composition study by using FESEM-EDX showed no significant changes in the composition of elements (C, Co and Cl) in the freshly fabricated electrode and after electrolysis of synthetic textile effluent. This showed that the fabricated electrode has a high mechanical strength and strong binding ability between C and Co due to the use of PVC as a binder.