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Surface-decorated macadamia (Macadamia sp.) nutshells for the detoxification of chromium(VI) polluted water.Moyo, Malvin 02 1900 (has links)
Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Driven by the need for sustainably sourced catalysts and the use of reaction systems that generate environmentally benign by-products, the present study aimed to deposit stable, dispersed palladium (Pd) nanoparticles on the modified surfaces of granular macadamia nutshell (MNS) biomass for catalytic reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)]. Through wet impregnation with Pd(II) ions and subsequent hydrazinemediated reduction to Pd(0), Pd nanoparticles were embedded in a scaffold of polyethyleneimine grafted on bleached MNS previously coated with a chemically bound layer of polyglycidyl methacrylate.
Visualization and imagery from scanning electron microscopy showed the formation of different layers of the polymeric coating and dispersed palladium resulting from surface modification and palladium nanoparticle synthesis, respectively. X-ray diffraction, energy-dispersive X-ray spectroscopic, and X-ray photoelectron spectroscopic analysis confirmed the formation of Pd on the modified MNS surface. An estimate of 5.0 nm for crystallite size was calculated by application of the Scherrer equation.
The composite material, denoted Pd@PEI-MNS, exhibited catalytic activity in formic acidmediated Cr(VI) reduction. Through a one-factor-at-a-time experimental design, the activity of the Pd@PEI-MNS was illustrated to be dependent on solution pH; initial Cr(VI) concentration, initial formic acid concentration, and presence of competing anions; Pd@PEI-MNS dose; and temperature. Subsequent modeling of the Cr(VI) removal process by response surface methodology revealed that the most influential factor was Pd@PEI-MNS dose followed by temperature and formic acid concentration. The influence of initial Cr(VI) concentration, was surpassed by the dose-temperature and dose-formic acid concentration interactive effects.
Elucidation of the Cr(VI) removal mechanism by XPS and FTIR demonstrated the active participation of surface –CH2OH functional groups, the bulk of which originated from the reduction of esters of the grafted ligands. Replacement of formic acid with hydrochloric acid in the reaction medium limited the Cr(VI) removal process to adsorption with non-extensive redox reaction with –CH2OH groups. Where the redox reactions converted formic acid to carbon dioxide, the –CH2OH groups were converted to –COO– groups.
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Humic acid pretreatment for enhancing microbial removal of metals from a synthetic 'wastewater'.Desta, Tsegazeab Goje. January 2004 (has links)
The presence of heavy metal ions in waste streams is one of the most pervasive
environmental issues of present times. A rotating biological contactor (RBC) was used
to investigate the potential capacity of microbial biofilms in remediation of the metal
ion species from a mixed metal contaminated effluent solution containing Cr+3
, Pb+2
and Cu+2
, each at a concentration of 200 mg r1
• In the first part of this study the
effectiveness of various support materials for the development of microbial biofilms
capable of removing heavy metals from a synthetic effluent was investigated. EDX
analysis showed that none of the support matrices investigated, viz. gravel, polyester
batting and sand, adsorbed metal ions on their surfaces; hence, metal adsorption was
due purely to microbial activities. The biofilms attached more firmly and uniformly to
polyester batting than to gravel and sand. The characteristics of polyester batting which
made it a superior support matrix were its surface roughness and porous hydrophilic
nature, which provided a larger surface area for the adhesion of microorganisms and
attraction of nutrients during the biofilm development process.
The selective accumulation of metal ion specIes by various microbial populations
grown as biofilm using polyester batting as support matrix in separate compartments of
a single-stage RBC bioreactor was examined. Lead ions were readily accumulated by
almost all the microbial biofilms tested. Fungus-dominated biofilms selectively
accumulated chromium ions whereas biofilms comprising mainly bacteria more readily
accumulated copper ions from the mixed metal contaminated effluent solution.
However, where interactions between the bacterial and fungal components were
encouraged the mechanical stability of the biofilms was enhanced so that large amounts
of all three metal ion species were removed by this biofilm.
The combined effect of a series of bench-scale columns containing liquid humic acid
and a three stage RBC bioreactor on the removal of metal ion species from a mixed
metal contaminated effluent was investigated. After seven days of treatment the
combined system had removed approximately 99% of the Cr+3, 98% of the Pb+2 and 90% of the Cu+2 ions from the mixed metal contaminated synthetic effluent.
Complexation of the metal ions with humic acid was the predominant factor accounting
for approximately 68-86% Cr+3
, 70-86% Pb+2 and 53-73% Cu+2 removal levels within
the columns. A large proportion of the remaining Cr+3 and Pb+2, but not of the Cu+2,
was removed in compartment 1 of the RBC. This suggested that the presence of the
former two metals in solution might have reduced the removal of the Cu+2 ions from the
system. The removal of substantially large amounts of the competing ions chromium
and lead during the initial stages of the treatment process meant that copper was
successfully taken up in the second and third RBC compartments. Hence, the economy
of the treatment process was improved as larger quantities of the metal ions were
removed in a shorter period of time than was possible when using the individual
treatments (humic acid-metal complexation and biofilm adsorption) separately. More
than 75%,92% and 86% of the adsorbed Cr+3
, Pb+2 and Cu+2 ions, respectively, were
recovered from the three RBC bioreactor compartments following repeated washing of
the biofilms with 0.1 M HCI. This relatively easy desorption suggested that the metal
ions were simply adsorbed onto the surfaces of the biofilm cells rather than being taken
into the cytoplasm of the cells. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.
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Surface-decorated macadamia (Macadamia sp.) nutshells for the detoxification of chromium(VI) polluted waterMoyo, Malvin 02 1900 (has links)
Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Driven by the need of sustainably sourced catalysts and the use of reaction systems that generate environmentally benign by-products, the present study aimed to deposit stable, dispersed palladium (Pd) nanoparticles on the modified surfaces of granular macadamia nutshell (MNS) biomass for catalytic reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)]. Through wet impregnation with Pd(II) ions and subsequent hydrazine-mediated reduction to Pd(0), Pd nanoparticles were embedded in a scaffold of polyethyleneimine grafted on bleached MNS previously coated with a chemically bound layer of polyglycidyl methacrylate.
Visualization and imagery from scanning electron microscopy showed the formation of different layers of the polymeric coating and dispersed palladium resulting from surface modification and palladium nanoparticle synthesis, respectively. X-ray diffraction, energy-dispersive X-ray spectroscopic analysis confirmed the formation of Pd on the modified MNS surface. An estimate of 5.0 nm for crystallite size was calculated by application of the Scherrer equation.
The composite material, denoted Pd@PEI-MNS, exhibited catalytic activity in formic acid-mediated Cr(VI) reduction. Through a one-factor-at-a-time experimental design, the activity of the Pd@PEI-MNS was illustrated to be dependent on solution pH; initial Cr(VI) concentration, initial formic acid concentration, and presence of competing anions; Pd@PEI-MNS dose; and temperature. Subsequent modeling of the Cr(VI) removal process by response surface methodology revealed that the most influential factor was Pd@PEI-MNS dose followed by temperature and formic acid concentration. The influence of initial Cr(VI) concentration, was surpassed by the dose-temperature and dose-formic acid concentration interactive effects.
Elucidation of the Cr(VI) removal mechanism by XPS and FTIR demonstrated the active participation of surface -CH2OH functional groups, the bulk of which originated from the reduction of esters of the grafted ligands. Replacement of formic acid to carbon dioxide, the -CH2OH groups were converted to -COO- groups.
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