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Heavy metal contamination in aquatic ecosystems worsens due to rapid industrial expansion. Biochar, an efficient and economical adsorbent, has attracted much interest in environmental science, particularly in removing heavy metals (HMs). The paper covers basic details on biochar, its preparation, and potential chemical and inorganic modifications. Possible adsorption mechanisms of HMs on biochar, which include electrostatic attraction, ion exchange, surface complexation, chemical precipitation, and hydrogen bonding, are also discussed. These mechanisms are affected by the type of biochar used and the species of HMs present. Research findings suggest that while biochar effectively removes HMs, modifications to the carbon-rich hybrid can enhance surface properties such as surface area, pore size, functional groups, etc., and magnetic properties in a few cases, making them more efficient in HM removal. The choice of feedstock materials is one of the key parameters influencing the sorption capacity of biochars. This review aims to investigate the use of various forms of water hyacinth (WH), including aquatic plants, biomass, biochar, and modified biochar, as effective adsorbents for removing HMs from aqueous solutions and industrial effluents through a comparative analysis of their adsorption processes. However, further studies on the diverse effects of functional groups of modified biochar on HMs adsorption are necessary for future research.
RESUMEN
Plasma polymerized (PP) methyl acrylate (MA) and vinyl acetate (VA) composite thin films were deposited onto glass substrate varying MA and VA monomer concentrations. Thickness of the composite polymers is observed to vary on the MA and VA monomer ratios, where MA is found more reactive. The FESEM images of the composite polymers show better surface morphology compared to those of the homopolymers. Appearance of broad absorption bands in the FTIR spectra of polymer indicates the structural changes compared to monomer during polymerization. Thermogravimetric analysis and differential scanning calorimetry indicate that composite films are thermally more stable (up to 617 K) compared to homopolymer thin films (563 K). The current density versus voltage (J-V) characteristics of PP(MA-VA) composite films (sandwiched between aluminum electrodes) with different MA and VA ratios showed that the J values of the composite films gradually increase with elevating VA monomer and also with temperature (298-373 K). On the other hand, this value increases with decreasing the thickness of the composite films, which complies with the other studies. The conduction of the thickness-dependent composite films showed Ohmic in nature in the lower voltage region (< 10 V) while the space charge-limited conduction is found to be dominated in the higher voltage region (> 10 V) operating over the entire range of temperature. The activation energy at room temperature was found to be ~ 0.019 eV in the Ohmic region and 0.260 eV in the non-Ohmic region.
RESUMEN
Low-pressure (33.33 Pa) plasma polymerized methyl acrylate and vinyl acetate composite thin films with various monomer compositions were deposited onto glass substrates. Under the same plasma conditions, the homopolymer thin films were also prepared. The thickness of the composite films was observed to vary between 117 and 213 nm depending on the monomer ratio. The composite films exhibit a smooth, pinhole-free, and immaculate surface morphology, surpassing that of the homopolymers. The energy dispersive x-ray study shows that the films contain mainly carbon and oxygen with 26.09-37.20 at% and 35.03 - 40.10 at%, respectively. The composite films contain more carbon contents which enhance the film stability. The appearance of some broad absorption bands in the Fourier transform infrared spectroscopy indicates structural changes in the PP films caused by the restructuring or dilapidation of monomer molecules while forming the polymer. The UV-visible spectra analysis reveal that the composite films exhibited a tunable optical band gap by adjusting the monomer ratio. The decrease of methyl acrylate monomer reduces the direct and indirect optical band-gap values of composite films from 3.15 to 3.00 eV and 2.35 to 1.74 eV, respectively. While Urbach energy values increases from 0.33 eV to 0.90 eV. All the films showed good transmittance properties (86 - 96%) in the visible range wavelength (550 - 800 nm). Other optical parameters are also found better in composite films which indicates the aptness of the composite films in various optoelectronic or electronic applications.
RESUMEN
Studies on Mg substituted Zn-Cu ferrites with chemical formula of Zn0.6Cu0.4-xMgxFe2O4 were synthesized by solid-state reaction technique. The structural phase of all the samples is characterized by XRD, show single phased cubic spinel structure. Density of the samples increases with the increase of Mg quantity. Average grain diameter decreases with increasing Mg content. All samples show soft ferromagnetic behavior as confirmed from the M-H hysteresis loop obtained from the VSM analysis. Thesaturation magnetization decreases with increasing Mg quantity. Increasing and decreasing trend of coercivity with the increase of Mg quantityis observed, which led to the slightly hard magnetic phase. The high frequencies create more effective for the ferrite grains of advanced conductivity and minor dielectric constant for all the samples but the AC electrical resistivity and dielectric constant are initiate to be more operational at lower frequencies. The variation of resistivity, dielectric constant with the Mg concentration is completely related to the porosity and bulk density.