Performance of magnetic nanocomposites for the removal of some selected contaminants from aqueous solution
- Authors: Ojemaye, Mike Onyewelehi
- Date: 2017
- Subjects: Nanocomposites (Materials)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/8746 , vital:33508
- Description: In this thesis, the performances of magnetic nanoparticles based materials were assessed for the removal or reduction of heavy metals in aqueous solutions. The successful synthesis of a novel adsorbent, azomethine functionalized magnetic nanoparticles (MNP-Maph) by covalent bonding between the amine group (-NH2) of amine functionalized magnetic nanoparticles (MNP-NH2) and carboxylic group (-COOH) of 4-{[(E)-phenylmethylidene]amino}benzoic acid (Maph-COOH) was achieved. This adsorbent was examined for the removal of di and trivalent ions (Cu2+, Zn2+, As3+, Pb2+ and Hg2+) from aqueous solutions. Also, magnetic photocatalyst with silica interlayer (NiFe2O4-SiO2-TiO2) was synthesized and employed for the reduction of Cr(VI) in aqueous solution. The photocatalytic reduction efficiency of this material was compared with that of magnetic titanium dioxide (NiFe2O4-TiO2) photocatalyst and titanium dioxide (TiO2) to ascertain the material with the best photocatalytic efficiency and ease of separation. All synthesized materials were characterized by using XRD, FT-IR, TEM, SEM, TGA and VSM before application. For the adsorption processes, the effects of pH, contact time, adsorbent dose and temperature were examined to ascertain the experimental condition necessary for the optimal removal of metal ions from solution. The data obtained from all experiments were fitted into four kinetic models; pseudo-first order, pseudo-second order, elovich and intra particle diffusion models to determine the mechanism involved in the adsorption of these di and trivalent ions while two isotherm models were employed in the adorption processes; these include: Langmuir and Freudlich models. Also, for the photocatalytic experiment, the effects of pH, contact time and photocatalyst dose were investigated to determine the experimental conditions necessary for the optimal reduction of Cr(VI) in aqueous solution. MNP-Maph showed excellent removal capacities of 34.08, 35.83, 50.08, 58.24 and 59.24 mg g-1 for Cu2+, Zn2+, As3+, Pb2+ and Hg2+ respectively compared to data previously reported in literature. This is as a result of the high affinity of azomethine group towards metal ions which tremendously enhanced removal of metal ions by adsorption. The incorporation of azomethine to magnetic nanoparticles improved the affinity towards metal ions removal forming strong electrostatic interaction between the adsorbent active sites and adsorbates. Also, the utilization of NiFe2O4-SiO2-TiO4, NiFe2O4-TiO2 and TiO2 for the reduction of Cr(VI) in aqueous solution showed a good photocatalytic performance with NiFe2O4-SiO2-TiO2 showing to be better in terms of both photocatalytic reduction and magnetic separation. TiO2 was observed to have 96.7percent reduction efficiency within 240 min while NiFe2O4-SiO2-TiO2 has 96.5percent reduction efficiency within 300 min and NiFe2O4-TiO2 gave 60percent reduction efficiency within 300 min of UV irradiation. This magnetic photocatalyst composite (NiFe2O4-SiO2-TiO2) gives the advantage of avoiding the problem of separation often encountered with most photocatalyst materials including TiO2 by allowing separation with the aid of a magnetic field. The adsorption processes were all described by pseudo-second order and Langmuir isotherm models while the photocatalytic process was described by Langmuir-Hinshelwood (L-H) kinetic model. Furthermore, thermodynamic experiment studied for the adsorption processes showed that all metal ion adsorption except Hg2+ by MNP-Maph were endothermic in nature, rapid and spontaneous indicating the feasibility of the sorbent material for the removal of metal ions from aqueous solutions. Also, regenerability study conducted to determine the reusability of sorbent material after seven cycles showed the potential to reuse sorbent material seven times or more. The reusability of the sorbent material was observed to show a percentage of an average of 78percent using 50:50 mixture of 0.1 mol dm-3 HNO3 and HCl for all adsorption processes. For the photocatalytic experiment, regenerability using 0.1 mol dm-3 for 1 h was observed to be very impressive after 3 runs for all synthesized photocatalytic materials. This thereby implies that the removal of metal ions by these materials will not in any way introduce secondary pollutants into the environment. Rather, it will avert the production of secondary pollutants. Also, the use of simple conventional chemicals for the regeneration of synthesized materials showed that regeneration in this study is cost effective as regeneration has been known to cost about three quarter of the total operation and maintenance of an adsorption or photocatalytic process. Application of MNP-Maph to real wastewater sampled from five different wastewater treatment plants in Eastern Cape Province for the removal of Cu2+, Zn2+ and As3+ showed that removal efficiencies of approximately 80 percent were achieved for all three metal ions upon adsorption by MNP-Maph. These therefore show that the introduction of metal loving ligand such as Maph-COOH improved the efficiency of MNP towards the removal of heavy metal ions from aqueous solution. Also, silica positively influenced the performance of magnetic titanium dioxide towards Cr(VI) reduction and separation from aqueous solution. This study therefore showed that these materials should be considered for future applications in the area of water/wastewater decontamination.
- Full Text:
- Date Issued: 2017
- Authors: Ojemaye, Mike Onyewelehi
- Date: 2017
- Subjects: Nanocomposites (Materials)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/8746 , vital:33508
- Description: In this thesis, the performances of magnetic nanoparticles based materials were assessed for the removal or reduction of heavy metals in aqueous solutions. The successful synthesis of a novel adsorbent, azomethine functionalized magnetic nanoparticles (MNP-Maph) by covalent bonding between the amine group (-NH2) of amine functionalized magnetic nanoparticles (MNP-NH2) and carboxylic group (-COOH) of 4-{[(E)-phenylmethylidene]amino}benzoic acid (Maph-COOH) was achieved. This adsorbent was examined for the removal of di and trivalent ions (Cu2+, Zn2+, As3+, Pb2+ and Hg2+) from aqueous solutions. Also, magnetic photocatalyst with silica interlayer (NiFe2O4-SiO2-TiO2) was synthesized and employed for the reduction of Cr(VI) in aqueous solution. The photocatalytic reduction efficiency of this material was compared with that of magnetic titanium dioxide (NiFe2O4-TiO2) photocatalyst and titanium dioxide (TiO2) to ascertain the material with the best photocatalytic efficiency and ease of separation. All synthesized materials were characterized by using XRD, FT-IR, TEM, SEM, TGA and VSM before application. For the adsorption processes, the effects of pH, contact time, adsorbent dose and temperature were examined to ascertain the experimental condition necessary for the optimal removal of metal ions from solution. The data obtained from all experiments were fitted into four kinetic models; pseudo-first order, pseudo-second order, elovich and intra particle diffusion models to determine the mechanism involved in the adsorption of these di and trivalent ions while two isotherm models were employed in the adorption processes; these include: Langmuir and Freudlich models. Also, for the photocatalytic experiment, the effects of pH, contact time and photocatalyst dose were investigated to determine the experimental conditions necessary for the optimal reduction of Cr(VI) in aqueous solution. MNP-Maph showed excellent removal capacities of 34.08, 35.83, 50.08, 58.24 and 59.24 mg g-1 for Cu2+, Zn2+, As3+, Pb2+ and Hg2+ respectively compared to data previously reported in literature. This is as a result of the high affinity of azomethine group towards metal ions which tremendously enhanced removal of metal ions by adsorption. The incorporation of azomethine to magnetic nanoparticles improved the affinity towards metal ions removal forming strong electrostatic interaction between the adsorbent active sites and adsorbates. Also, the utilization of NiFe2O4-SiO2-TiO4, NiFe2O4-TiO2 and TiO2 for the reduction of Cr(VI) in aqueous solution showed a good photocatalytic performance with NiFe2O4-SiO2-TiO2 showing to be better in terms of both photocatalytic reduction and magnetic separation. TiO2 was observed to have 96.7percent reduction efficiency within 240 min while NiFe2O4-SiO2-TiO2 has 96.5percent reduction efficiency within 300 min and NiFe2O4-TiO2 gave 60percent reduction efficiency within 300 min of UV irradiation. This magnetic photocatalyst composite (NiFe2O4-SiO2-TiO2) gives the advantage of avoiding the problem of separation often encountered with most photocatalyst materials including TiO2 by allowing separation with the aid of a magnetic field. The adsorption processes were all described by pseudo-second order and Langmuir isotherm models while the photocatalytic process was described by Langmuir-Hinshelwood (L-H) kinetic model. Furthermore, thermodynamic experiment studied for the adsorption processes showed that all metal ion adsorption except Hg2+ by MNP-Maph were endothermic in nature, rapid and spontaneous indicating the feasibility of the sorbent material for the removal of metal ions from aqueous solutions. Also, regenerability study conducted to determine the reusability of sorbent material after seven cycles showed the potential to reuse sorbent material seven times or more. The reusability of the sorbent material was observed to show a percentage of an average of 78percent using 50:50 mixture of 0.1 mol dm-3 HNO3 and HCl for all adsorption processes. For the photocatalytic experiment, regenerability using 0.1 mol dm-3 for 1 h was observed to be very impressive after 3 runs for all synthesized photocatalytic materials. This thereby implies that the removal of metal ions by these materials will not in any way introduce secondary pollutants into the environment. Rather, it will avert the production of secondary pollutants. Also, the use of simple conventional chemicals for the regeneration of synthesized materials showed that regeneration in this study is cost effective as regeneration has been known to cost about three quarter of the total operation and maintenance of an adsorption or photocatalytic process. Application of MNP-Maph to real wastewater sampled from five different wastewater treatment plants in Eastern Cape Province for the removal of Cu2+, Zn2+ and As3+ showed that removal efficiencies of approximately 80 percent were achieved for all three metal ions upon adsorption by MNP-Maph. These therefore show that the introduction of metal loving ligand such as Maph-COOH improved the efficiency of MNP towards the removal of heavy metal ions from aqueous solution. Also, silica positively influenced the performance of magnetic titanium dioxide towards Cr(VI) reduction and separation from aqueous solution. This study therefore showed that these materials should be considered for future applications in the area of water/wastewater decontamination.
- Full Text:
- Date Issued: 2017
Combating corruption while respecting human rights : a critical study of the non-conviction based assets recovery mechanism in Kenya and South Africa
- Authors: Obura, Ken Otieno
- Date: 2014
- Subjects: Human rights -- Kenya , Human rights -- South Africa , Corruption -- Kenya , Corruption -- South Africa , Reparation (Criminal justice) -- Kenya , Reparation (Criminal justice) -- South Africa , Political corruption -- Kenya , Political corruption -- South Africa , Corruption investigation -- Kenya , Corruption investigation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3719 , http://hdl.handle.net/10962/d1013159
- Description: The thesis contributes to the search for sound anti-corruption laws and practices that are effective and fair. It argues for the respect for human rights in the crafting and implementation of anti-corruption laws as a requisite for successful control of corruption. The basis for this argument is threefold: First, human rights provide a framework for checking against abuse of state’s police power, an abuse which if allowed to take root, would make the fight against corruption lose its legitimacy in the eye of the people. Second, human rights ensure that the interest of individuals is catered for in the crafting of anti-corruption laws and practices thereby denying perpetrators of corruption legal excuses that can be exploited to delay or frustrate corruption cases in the courts of law. Third, human rights provide a useful framework for balancing competing interests in the area of corruption control – it enables society to craft measures that fulfils the public interest in the eradication of corruption while concomitantly assuring the competing public interest in the protection of individual members’ liberties – a condition that is necessary if the support of the holders of these competing interests is to be enlisted and fostered in the fight against corruption. The thesis focuses on the study of the non-conviction based assets recovery mechanism, a mechanism that allows the state to apply a procedure lacking in criminal law safeguards to address criminal behaviour. The mechanism is thus beset with avenues for abuse, which if unchecked could have debilitating effects not only to individual liberties but also to the long term legitimacy of the fight against corruption. In this regard, the thesis examines how the human rights framework has been used in Kenya and South Africa to check on the potential dangers of the non-conviction based mechanism and to provide for a proportional balance between the imperative of corruption control and the guarantee against arbitrary deprivation of property. The aim is to unravel the benefits of respecting human rights in the fight against corruption in general and in the non-conviction based assets recovery in particular. Kenya and South Africa are chosen for study because they provide two models of non-conviction based mechanisms with different levels of safeguards, for comparative consideration.
- Full Text:
- Date Issued: 2014
- Authors: Obura, Ken Otieno
- Date: 2014
- Subjects: Human rights -- Kenya , Human rights -- South Africa , Corruption -- Kenya , Corruption -- South Africa , Reparation (Criminal justice) -- Kenya , Reparation (Criminal justice) -- South Africa , Political corruption -- Kenya , Political corruption -- South Africa , Corruption investigation -- Kenya , Corruption investigation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3719 , http://hdl.handle.net/10962/d1013159
- Description: The thesis contributes to the search for sound anti-corruption laws and practices that are effective and fair. It argues for the respect for human rights in the crafting and implementation of anti-corruption laws as a requisite for successful control of corruption. The basis for this argument is threefold: First, human rights provide a framework for checking against abuse of state’s police power, an abuse which if allowed to take root, would make the fight against corruption lose its legitimacy in the eye of the people. Second, human rights ensure that the interest of individuals is catered for in the crafting of anti-corruption laws and practices thereby denying perpetrators of corruption legal excuses that can be exploited to delay or frustrate corruption cases in the courts of law. Third, human rights provide a useful framework for balancing competing interests in the area of corruption control – it enables society to craft measures that fulfils the public interest in the eradication of corruption while concomitantly assuring the competing public interest in the protection of individual members’ liberties – a condition that is necessary if the support of the holders of these competing interests is to be enlisted and fostered in the fight against corruption. The thesis focuses on the study of the non-conviction based assets recovery mechanism, a mechanism that allows the state to apply a procedure lacking in criminal law safeguards to address criminal behaviour. The mechanism is thus beset with avenues for abuse, which if unchecked could have debilitating effects not only to individual liberties but also to the long term legitimacy of the fight against corruption. In this regard, the thesis examines how the human rights framework has been used in Kenya and South Africa to check on the potential dangers of the non-conviction based mechanism and to provide for a proportional balance between the imperative of corruption control and the guarantee against arbitrary deprivation of property. The aim is to unravel the benefits of respecting human rights in the fight against corruption in general and in the non-conviction based assets recovery in particular. Kenya and South Africa are chosen for study because they provide two models of non-conviction based mechanisms with different levels of safeguards, for comparative consideration.
- Full Text:
- Date Issued: 2014
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