Removal of Cu(II)-EDTA complex using TiO2/solar light: the effect of operational parameters and feasibility of solar light application

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Removal of chelated heavy metals from aqueous solution: A review of current methods and mechanisms

Water contamination with heavy metal ions and organic compounds such as citrate, ethylenediaminetetraacetic acid, tartrate, pharmaceuticals, surfactants and natural organic matter, is a serious problem in the natural environment. Although many methods have been effectively applied to the removal of heavy metal complexes from aqueous solution, there is a lack of information available on the mechanisms, advantages and disadvantages of these various methods. This review summarizes the various treatment methods applied to the removal of heavy metal complexes, with a summary of the mechanisms of action and recent research progress. The methods reviewed in detail include electrolysis, membrane separation, adsorption, precipitation, replacement-coprecipitation, TiO₂ photocatalysis and Fenton oxidation-precipitation, with the advantages and disadvantages of each method discussed. Furthermore, the heavy metal complex removal mechanisms are analyzed comprehensively. Results show that the adsorption method exhibited unique merits, showing much promise for future development. Finally, this review comprehensively analyzes future prospects and developments in methods for removal of chelated heavy metals.

Green approach for photocatalytic Cu(II)-EDTA degradation over TiO2: toward environmental sustainability

A green approach was successfully developed to reap three environmental benefits simultaneously: (1) clean water production, (2) hydrogen (H2) generation, and (3) well-dispersed in situ Cu(2+) recovery for direct TiO2-CuO composite reclamation, by exploiting the synergistic integration of photocatalytic reaction of Cu-EDTA and one-dimensional (1D) ultralong and ultrathin TiO2 nanofibers. In this light-initiated system, Cu-EDTA was oxidized by TiO2 thus releasing Cu(2+) which was reduced and recovered through uniform adsorption onto the long and porous TiO2 surface. A win-win platform was thus attained, on which Cu was recovered while providing active sites for H2 generation via photoreduction of H2O and enhancing photo-oxidation of remaining intermediate oxidation byproducts. Experimental results showed a H2 generation rate of 251 μmol/h concomitantly with TOC reduction. The used TiO2 nanofibers deposited with Cu were reclaimed directly as the TiO2-CuO composite after a facile heat treatment without additional chemicals and subsequently reusable for photocatalytic treatment of other wastewater (glycerol) to cogenerate H2 and clean water under both UV-visible and visible light. This study expounds a significant advancement through an ingenious integration which enhances the environmental sustainability of Cu-EDTA treatment via TiO2 photocatalysis. It also represents a promising and adoptable approach to synthesize other functional composite nanomaterials in a green manner thus broadening its environmental application spectrum, as it promotes industrial environmental management via waste segregation and motivates research to recover more resources from wastewater.

Effects of the density of carboxyl groups in organic compounds on the photocatalytic reduction of Cr(VI) in a TiO2 suspension

Photocatalytic reduction (PCR) of Cr(VI) in a TiO2 suspension was studied at pH 4 in the presence of organic compounds containing different numbers of carboxyl groups. The compounds studied were glycine (Gly), iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA). In all the cases, near complete Cr(VI) removal was observed after 60 minutes. During PCR process, the aqueous Cr(VI) concentration measured with both Ion Chromatography and Atomic Absorption Spectrophotometery was different in the presence of IDA and EDTA as reaction proceeded while little difference was observed in a control test. This result suggests that a greater portion of reduced Cr(III) species was possibly dissolved through complex formation with IDA (Cr(III)-IDA) and EDTA (Cr(III)-EDTA) or with reaction intermediates (Cr(III)-organic complexes) during PCR compared to the control test. As the number of carboxyl group increased Cr(VI) reduction increased and showed a good linear relationship between initial rates of Cr(VI) reduction and adsorption density of carboxyl group of the surface of TiO2. The initial rate of Cr(VI) reduction in the presence of EDTA was 5 times greater than that in control. When the PCR process was applied in the treatment of real wastewater, an effective Cr(VI) reduction was observed with addition of EDTA.

Treatment of wastewater containing Cu(II)-EDTA using immobilized TiO2/solar light

The photocatalytic oxidation (PCO) of Cu(II)-ethylene diamine tetra-acetic acid (EDTA), employing immobilized TiO2, under natural sunlight rather than artificial UV light conditions, was investigated at a latitude 38 degrees. The immobilized TiO2 film was prepared using a sol gel process, the crystalline structure of which was identified, by X-ray diffraction analysis, as a mixture of the rutile and anatase forms. The PCO of Cu(II)-EDTA was examined in a circulating reactor with 20 L of 10(-4) M Cu(II)-EDTA and synthetic and real wastewaters at pH 4 and 6.5, respectively. The removals of both Cu(II) and DOC were initially relatively rapid, but slowed as the reaction proceeded and generally followed first-order kinetics. The rate constants for the removal of Cu(II) and DOC were 1.1 x 10(-3) and 1.6 x 10(-3) min-1, respectively. The efficiency of the PCO in the decomplexation of Cu(II)-EDTA increased with increasing H2O2 dose using both the synthetic and real wastewaters. Therefore, we suggest the PCO process using the solar/immobilized TiO2 system, with addition of H2O2 as well as filtration for the removal of suspended solids, can be effectively applied to the treatment of Cu(II)-EDTA containing real wastewater.