Emerging plastic litter variants: A perspective on the latest global developments.

Plastic litter is one of key reasons of environmental concern due to its adverse effect on ecosystem and health. Exposure of plastic litter to anthropogenic and ecological conditions results in a variety of emerging litter variants that fluctuate in composition, mechanical, and chemical properties. Considering the properties of these plastic litter variants, it is anticipated that the transportation of foreign species or microbial pathogens together with these litter variants is most likely to affect the marine ecosystem. Moreover the plastic litter may enter the plastic cycle or marine biota and can spread across the ocean. Very recently several emerging plastic litter variants such as anthropoquinas, plasticrust, pyroplastic, plastitar, and plastiglomerate have been reported along the coastal areas across the oceans. The purpose of this perspective is to comprehend these emerging plastic litter variants, integrate the latest developments and highlight their adverse effects on the coastal ecosystem. Further, it details the make-up, place of origin, and management strategies for these plastic litter variants.

Empirical Modeling of Electron Transport in Fe/Ti Layered Double Hydroxide Using Exponential, Gaussian and Mixed Gauss-Exponential Distribution.

Fe/Ti-layered double hydroxide (LDH) has been hydrothermally prepared and characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and UV-visible diffuse reflectance spectroscopy for evaluation of its structure, morphology, and optical properties. The purpose of doping Ti4+ with Fe3+ toward the synthesis of Fe/Ti LDH is to extend the absorption of the nanomaterial to longer wavelength, which is known to exhibit higher electron transport performance. To provide a practical realization, electron transport modeling across the band gap has been interpreted using exponential, Gaussian, and mixed Gauss-exponential distribution. The conduction band energy (E C) has been calculated by using the observed values of band gap (E g) and ξ-potential of the LDH. A detailed study has been undertaken to investigate the pattern of theoretical density of the LDH on the basis of unknown (E C = 0) and known (calculated) values of E C. Fermi-Dirac statistics has been used extensively for estimating the occupancy probability of electron (e-)-hole (h+) pair formation within the valence and conduction bands, respectively, with different temperatures, as well as for given energy levels. Monte Carlo simulations have also been performed to evaluate the suitability of the choice of the model, on the basis of the probability of availability of e-s within the conduction band. To provide a practical realization of the suggested models, electronic transition across the band gap of Fe/Ti LDH has been extensively investigated.

Synthesis and characterization of Mn/Co/Ti LDH and its utilization as a photocatalyst in visible light assisted degradation of aqueous Rhodamine B.

Luminescent Mn/Co/Ti LDH, synthesized by a single step hydrothermal route, has been found to be optically responsive for utilization as a highly efficient photocatalyst in destruction of the cationic dye Rhodamine B, in aqueous solution under visible light irradiation. The material has been found to be better than the commercial catalysts like MnO, CoO, TiO2 and Degussa P25. Multiple techniques like XRD, XPS, FT-IR, EIS, TG, UV-visible DRS, PL, TRES, N2-sorption-desorption, dynamic light scattering, TEM-EDS and AFM analyses were used to characterize the LDH. The results indicated Mn/Co/Ti LDH to have a multilayered crystalline structure with hexagonal morphology that carries metal ions in mixed valences, oxygen vacancies, defect states, thermal stability, narrow band gap, high surface area, and electrostatic surface charge variation with pH. The photocatalytic activity of the LDH could be co-related with the structural aspects such as oxidation states, narrow band gap, high surface area and existence of defects. The active species responsible for photocatalysis have been evaluated with EPR, terephthalic acid fluorescence probe and indirect radical-hole trapping experiments. The photodegradation mechanism involves electron and hole hopping across the material and also photosensitization of the dye. Ex situ 1H-NMR and GC-MS analyses of the colorless end products of Rhodamine B destruction provide further insight into the reaction mechanism. The complete mineralization of the decolorized end product of degradation was evaluated with TOC analysis. The results indicate the potential for using multi metal incorporated LDH in destroying dyes and their degradation products in industrial wastewater.

Ni/Ti layered double hydroxide: synthesis, characterization and application as a photocatalyst for visible light degradation of aqueous methylene blue.

Visible light responsive 2 : 1 Ni/Ti layered double hydroxide (LDH) was synthesized by a single step hydrothermal route using commercially available Ni(NO3)2·6H2O, TiCl4 and urea. The material exhibited significant absorption in the visible range with a very narrow band gap (2.68 eV). This could be attributed to structural defects as confirmed by diffuse reflectance spectroscopy (DRS), photoluminescence (PL), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. FT-IR, TGA, DTA, DSC, HR-TEM and SEM-EDX measurements yielded information about structural aspects, thermal stability and surface morphology. Surface and pore characteristics of the material were obtained from the BET isotherm for N2 adsorption at 77 K. Zeta potential measurements were used to characterize the electrical properties of the surface while XPS revealed changes in surface states and oxygen deficiencies. The material was found to be an excellent photocatalyst for the degradation of aqueous methylene blue in visible light. The photocatalytic properties of the material were explained on the basis of the narrow band gap, the high surface area and the presence of surface defects. The photocatalytic activity improved in alkaline media [pH 11.0, catalyst load 15 mg in 200 ml dye solution, dye concentration 1 × 10(-6) M (= 0.3198 mg L(-1))] due to the electrostatic attractions between the dye cations and the negative charges on the Ni/Ti LDH surface. The catalytic activity was found to be higher than the common commercial catalysts like ZnO, ZnS, NiO, TiO2 and Degussa P25. The catalytic activity was retained even after five methylene blue degradation cycles, demonstrating that the LDH could be an important addition to the field of wastewater treatment.

Synthesis and characterization of Co/Ti layered double hydroxide and its application as a photocatalyst for degradation of aqueous Congo Red.

2 : 1 Co/Ti layered double hydroxide (LDH) was synthesized hydrothermally using commercially available Co(NO3)2·6H2O and TiCl4, on a urea template. The high surface area material (~180 m2 g-1) had a narrow band gap (2.67 eV) and shallow and deep trap defect sites. The layered nanomaterial exhibited remarkable semiconductor properties and demonstrated excellent visible light decolourisation efficiency for the anionic dye Congo Red in aqueous medium. The photocatalytic efficiency of the LDH was better than common commercial materials in use such as ZnO, ZnS, NiO, CoO, TiO2 and Degussa P25. The presence of different surface states of defect sites in the LDH was confirmed by PL, EIS and XPS measurements. XRD, DRS, FT-IR, AFM, TEM, SEM/EDX and TG/DTG analyses yielded information about the structural, morphological properties and thermal stability of the LDH. BET N2 adsorption-desorption measurements at 77 K gave surface area and porosity data for the LDH. The surface charge characteristics of the LDH were evaluated with ξ-potential measurements over a wide pH-range in aqueous medium. The photocatalytic behaviour towards decolourisation of the dye was evaluated depending on the reaction variables of pH, LDH amount, initial dye concentration and effects of quenchers, and variation of molar ratios of Co/Ti LDH. The pseudo-first order model satisfactorily described the degradation kinetics of the anionic dye. The photocatalytic mechanistic pathways of the LDH were explained on the basis of an electron-hole (e--h+) hopping conduction model and also photosensitization of the dye. The maximum catalytic efficiency was observed with 15.0 mg of LDH at pH 4 for the anionic Congo Red dye at a concentration 1 × 10-5 M. The LDH was stable even after the fifth catalytic cycle, indicating its remarkable efficiency in potential decolourisation treatments. The dye degradation products were analysed with GC-MS and a reaction mechanism was proposed for the breakdown of the dye to simple and less toxic components.