Ihsan Khan | King Fahd University of Petroleum and Minerals (original) (raw)

Papers by Ihsan Khan

Bioinorganic Chemistry and Applications, 2017

Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) w... more Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25°C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models dem...

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Journal of Nanomaterials, 2016

In this paper, carbon nanotubes (CNTs) impregnated with iron oxide nanoparticles were employed fo... more In this paper, carbon nanotubes (CNTs) impregnated with iron oxide nanoparticles were employed for the removal of benzene from water. The adsorbents were characterized using scanning electron microscope, X-ray diffraction, BET surface area, and thermogravimetric analysis. Batch adsorption experiments were carried out to study the adsorptive removal of benzene and the effect of parameters such as pH, contact time, and adsorbent dosage. The maximum removal of benzene was 61% with iron oxide impregnated CNTs at an adsorbent dosage 100 mg, shaking speed 200 rpm, contact time 2 hours, initial concentration 1 ppm, and pH 6. However, raw CNTs showed only 53% removal under same experimental conditions. Pseudo-first-order kinetic model was found well to describe the obtained data on benzene removal from water. Initial concentration was varied from 1 to 200 mg/L for isotherms study. Langmuir isotherm model was observed to best describe the adsorption data. The maximum adsorption capacities we...

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Separation and Purification Technology, 2016

Abstract The scarcity of water, especially in arid and semi-arid regions of the world is exerting... more Abstract The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium, cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended.

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Toxicological & Environmental Chemistry, 2015

This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents incl... more This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents including carbon nanotubes (CNTs) and carbon nanofibers (CNFs); and micro-adsorbents including activated carbon (AC) and fly ash (FA). The materials were characterized by thermogravimetric analysis, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area, zeta potential, field emission scanning electron microscopy, and UV spectroscopy. The adsorption experimental conditions such as pH of the solution, agitation speed, contact time, initial concentration of phenol, and adsorbent dosage were optimized for their influence on the phenol. The removal efficiency of the studied adsorbents has the following order: AC > CNTs > FA > CNFs. The capacity obtained from Langmuir isotherm was found to be 1.348, 1.098, 1.007, and 0.842 mg/g of AC, CNTs, FA, and CNFs, respectively, at 2 hours of contact time, pH 7, an adsorbent dosage of 50 mg, and a speed of 150 rpm. The higher adsorption of phenol on AC can be attributed to its high surface area and its dispersion in water. The optimum values of these variables for maximum removal of phenol were also determined. The experimental data were fitted well to Langmuir than Freundlich isotherm models.

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Journal of Molecular Liquids, 2016

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Journal of Saudi Chemical Society, 2015

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Desalination and Water Treatment, 2015

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Journal of Molecular Liquids, 2015

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Journal of Molecular Liquids, 2015

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ABSTRACT The objective of this study was to maximize the conversion of saponification reaction in... more ABSTRACT The objective of this study was to maximize the conversion of saponification reaction in a continuous stirred tank reactor (CSTR). Full two-level factorial design and response surface methodology (RSM) were used t o d e t e r m i n e t h e optimum values of significant factors. The effect of five factors (sodium hydroxide and ethylacetate concentrations, feed ratio, agitation rate and temperature) was studied on the fractional conversion of sodium hydroxide (XNaOH). As a result of screening experiments, two factors (sodium hydroxide and ethylacetate concentrations) and their combined effect were found to be significant operating parameters for the saponification reaction in continuous stirred tank reactor (CSTR). The optimum values of these significant factors were also determined using response surface methodology (RSM). For maximum conversion of sodium hydroxide (XNaOH), i.e., 96.71%, the optimum values of sodium hydroxide and ethylacetate concentrations were found to be 0.01mol/L and 0.1 mol/L, respectively. Acorrelation was developed to show the relationship between different significant factors and response. The validity of the model was checked using analysis of variance (ANOVA). The experimental results are believed to be within reasonable accuracy and may be applicable for the improvement of such processes on industrial scale.

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Desalination and Water Treatment, 2015

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Arabian Journal for Science and Engineering, 2014

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Materials & Design, 2015

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Carbon nanomaterials have been extensively used in many applications owing to their unique therma... more Carbon nanomaterials have been extensively used in many applications owing to their unique thermal, electrical and mechanical properties. One of the prime challenges is the production of these nanomaterials on a large scale. This review paper summarizes the synthesis of various carbon nanomaterials via the chemical vapor deposition (CVD) method. These carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbide-derived carbon (CDC), carbon nano-onion (CNO) and MXenes. Furthermore, current challenges in the synthesis and application of these nanomaterials are highlighted with suggested areas for future research.

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Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) w... more Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25 ∘ C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models demonstrate good fitting for the adsorption data of toluene and p-xylene.

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The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pr... more The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium , cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended.

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In this work, a novel approach is used to synthesize an iron oxide doped carbon nanotube (CNT) me... more In this work, a novel approach is used to synthesize an iron oxide doped carbon nanotube (CNT) membrane, with the goal of fully utilizing the unique properties of CNTs. No binder is used for the synthesis of the membrane; instead , iron oxide particles serve as a binding agent for holding the CNTs together after sintering at high temperature. The produced membrane exhibited a high water flux and strong fouling resistance. In the first step, CNTs were impregnated with various loadings of iron oxide (1, 10, 20, 30 and 50%) via wet chemistry techniques. Impregnated CNTs were then compacted at 200 MPa and sintered at 1350 °C for 5 h to form a compact disc. The membranes were analysed by measuring their porosity, contact angle, diametrical compression test and water flux. The flux of pure water was observed to increase with an increase in iron oxide content. The permeate flux and rejection rate of sodium alginate (SA) were determined to predict the antifouling behaviour of the membrane. A maximum removal of 90 and 88% of SA was achieved for membranes with a 10 and 1% iron oxide content , respectively, after 3 h. A minor decline in the permeate flux was observed for all membranes after 4 h of operation.

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A novel approach was used to synthesize a silver doped-CNT membrane, with the aim of fully utiliz... more A novel approach was used to synthesize a silver doped-CNT membrane, with the aim of fully utilizing the anti-toxic properties of CNTs and silver. No binder was used for the synthesis of the membrane; instead, silver particles served as a binding material for the CNTs after sintering at high temperature. In the first step, CNTs were impregnated with different loadings of silver (1, 10 and 20 wt.%) via a wet chemistry technique. Impregnated CNTs were then compacted at 200 MPa and sintered at 800 °C for 3 h to form a compact disk (membrane). The powder materials were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray dif-fraction and thermogravimetric analysis, while the membranes were characterized by measuring their porosity, contact angle, diametrical compression test, pure water permeate flux and antibacterial properties. The affinity of the membranes to biofouling was studied using Escherichia coli (E. coli). The produced membrane showed a high water permeate flux and exhibited strong antibacterial properties. All of the membranes with different silver loadings were able to remove/kill 100% of the bacteria tested; however, the CNT membrane with 10% silver showed a superior performance to the others. All bacteria were removed/killed by the membrane with 10% silver loading after the suspension had passed for only 60 min. These membranes would be advantageous in a continuous filtration system for the removal of different contaminants from water via desalination, adsorption and sieving.

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This work reports a comprehensive study of the adsorption characteristics of cadmium(II) on modif... more This work reports a comprehensive study of the adsorption characteristics of cadmium(II) on modified structures of carbon nanotubes (CNTs), carbon nanofibres (CNFs), activated carbon (AC), and fly ash (FA). The characterization was performed using field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface analysis. Several experimental parameters; ad-sorbent dosage, pH, and agitation speed and contact time, were investigated for their effects on the adsorp-tion of cadmium(II) from water. The optimum conditions of 2 h of contact time, pH 7, 50 mg adsorbent dosage and 150 rpm rotational speed were observed. Models of first-order, second-order and pseudo-second-order were fitted to the experimental data, and pseudo-second-order kinetics were observed to describe the adsorption of cadmium(II) on these adsorbents. The adsorption behaviours of cadmium(II) were evaluated using the Freundlich and Langmuir isotherm models. The maximum adsorption capacities of the modified adsorbents were observed to be 2.02 mg/g, 1.98 mg/g, 1.22 mg/g and 1.58 mg/g, for CNTs, AC, CNFs and FA, as obtained from Langmuir isotherm models. It was determined that surface modification of the CNTs, CNFs, and AC enhanced their adsorption efficiency. The results obtained are promising for the use of these modified materials with respect to water purification applications.

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The present study addresses the application of raw and modified carbon nanotubes (CNTs) and activ... more The present study addresses the application of raw and modified carbon nanotubes (CNTs)
and activated carbon (AC) for the removal of hexavalent chromium (Cr(VI)) from aqueous
solution. Surfaces of both the adsorbents were modified by acid treatment. Nitric acid was
used to remove impurities and to introduce carboxylic functional groups on the surfaces of
CNTs and AC. Raw and modified adsorbents (CNTs and AC) were characterized by scanning
electron microscopy, Brunauer–Emmett–Teller surface area analysis, and thermogravimetric
analysis. The influence of adsorbent dosage, contact time, agitation speed, and solution pH
were evaluated on the Cr(VI) removal efficiency using batch adsorption experiments. The
optimum pH for maximum adsorption of Cr(VI) was found to be 3 and 4 for AC and CNTs,
respectively. Modified and raw AC were able to remove 99 and 92% of Cr(VI) ions, respectively,
at 75 mg adsorbent dosage, agitation speed of 200 rpm, initial Cr(VI) concentration of
1 mg/L, contact time of 4 h, and solution pH 3, while the removal of Cr(VI) ions recorded
maximum values of 87 and 80% for modified and raw CNTs under same treatment conditions.
However, acid modification of CNTs was found to have no major effect on the percentage
removal of Cr(VI) ions at low adsorbent dosage. Adsorption capacities of both the adsorbents
were determined using batch adsorption experiments and experimental data were described
by Langmuir and Freundlich adsorption isotherm models. However, Langmuir isotherm
model was able to best describe the adsorption of Cr(VI) ions on raw and modified forms of
CNTs and AC. Maximum adsorption capacity (qe) was found to be 2.024 and 1.805 mg/g for
raw and modified AC, while 1.021 and 0.964 mg/g for raw and modified CNTs.

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Bioinorganic Chemistry and Applications, 2017

Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) w... more Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25°C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models dem...

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Journal of Nanomaterials, 2016

In this paper, carbon nanotubes (CNTs) impregnated with iron oxide nanoparticles were employed fo... more In this paper, carbon nanotubes (CNTs) impregnated with iron oxide nanoparticles were employed for the removal of benzene from water. The adsorbents were characterized using scanning electron microscope, X-ray diffraction, BET surface area, and thermogravimetric analysis. Batch adsorption experiments were carried out to study the adsorptive removal of benzene and the effect of parameters such as pH, contact time, and adsorbent dosage. The maximum removal of benzene was 61% with iron oxide impregnated CNTs at an adsorbent dosage 100 mg, shaking speed 200 rpm, contact time 2 hours, initial concentration 1 ppm, and pH 6. However, raw CNTs showed only 53% removal under same experimental conditions. Pseudo-first-order kinetic model was found well to describe the obtained data on benzene removal from water. Initial concentration was varied from 1 to 200 mg/L for isotherms study. Langmuir isotherm model was observed to best describe the adsorption data. The maximum adsorption capacities we...

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Separation and Purification Technology, 2016

Abstract The scarcity of water, especially in arid and semi-arid regions of the world is exerting... more Abstract The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium, cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended.

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Toxicological & Environmental Chemistry, 2015

This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents incl... more This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents including carbon nanotubes (CNTs) and carbon nanofibers (CNFs); and micro-adsorbents including activated carbon (AC) and fly ash (FA). The materials were characterized by thermogravimetric analysis, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area, zeta potential, field emission scanning electron microscopy, and UV spectroscopy. The adsorption experimental conditions such as pH of the solution, agitation speed, contact time, initial concentration of phenol, and adsorbent dosage were optimized for their influence on the phenol. The removal efficiency of the studied adsorbents has the following order: AC > CNTs > FA > CNFs. The capacity obtained from Langmuir isotherm was found to be 1.348, 1.098, 1.007, and 0.842 mg/g of AC, CNTs, FA, and CNFs, respectively, at 2 hours of contact time, pH 7, an adsorbent dosage of 50 mg, and a speed of 150 rpm. The higher adsorption of phenol on AC can be attributed to its high surface area and its dispersion in water. The optimum values of these variables for maximum removal of phenol were also determined. The experimental data were fitted well to Langmuir than Freundlich isotherm models.

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Journal of Molecular Liquids, 2016

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Journal of Saudi Chemical Society, 2015

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Desalination and Water Treatment, 2015

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Journal of Molecular Liquids, 2015

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Journal of Molecular Liquids, 2015

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ABSTRACT The objective of this study was to maximize the conversion of saponification reaction in... more ABSTRACT The objective of this study was to maximize the conversion of saponification reaction in a continuous stirred tank reactor (CSTR). Full two-level factorial design and response surface methodology (RSM) were used t o d e t e r m i n e t h e optimum values of significant factors. The effect of five factors (sodium hydroxide and ethylacetate concentrations, feed ratio, agitation rate and temperature) was studied on the fractional conversion of sodium hydroxide (XNaOH). As a result of screening experiments, two factors (sodium hydroxide and ethylacetate concentrations) and their combined effect were found to be significant operating parameters for the saponification reaction in continuous stirred tank reactor (CSTR). The optimum values of these significant factors were also determined using response surface methodology (RSM). For maximum conversion of sodium hydroxide (XNaOH), i.e., 96.71%, the optimum values of sodium hydroxide and ethylacetate concentrations were found to be 0.01mol/L and 0.1 mol/L, respectively. Acorrelation was developed to show the relationship between different significant factors and response. The validity of the model was checked using analysis of variance (ANOVA). The experimental results are believed to be within reasonable accuracy and may be applicable for the improvement of such processes on industrial scale.

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Desalination and Water Treatment, 2015

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Arabian Journal for Science and Engineering, 2014

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Materials & Design, 2015

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Carbon nanomaterials have been extensively used in many applications owing to their unique therma... more Carbon nanomaterials have been extensively used in many applications owing to their unique thermal, electrical and mechanical properties. One of the prime challenges is the production of these nanomaterials on a large scale. This review paper summarizes the synthesis of various carbon nanomaterials via the chemical vapor deposition (CVD) method. These carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbide-derived carbon (CDC), carbon nano-onion (CNO) and MXenes. Furthermore, current challenges in the synthesis and application of these nanomaterials are highlighted with suggested areas for future research.

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Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) w... more Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25 ∘ C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models demonstrate good fitting for the adsorption data of toluene and p-xylene.

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The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pr... more The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium , cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended.

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In this work, a novel approach is used to synthesize an iron oxide doped carbon nanotube (CNT) me... more In this work, a novel approach is used to synthesize an iron oxide doped carbon nanotube (CNT) membrane, with the goal of fully utilizing the unique properties of CNTs. No binder is used for the synthesis of the membrane; instead , iron oxide particles serve as a binding agent for holding the CNTs together after sintering at high temperature. The produced membrane exhibited a high water flux and strong fouling resistance. In the first step, CNTs were impregnated with various loadings of iron oxide (1, 10, 20, 30 and 50%) via wet chemistry techniques. Impregnated CNTs were then compacted at 200 MPa and sintered at 1350 °C for 5 h to form a compact disc. The membranes were analysed by measuring their porosity, contact angle, diametrical compression test and water flux. The flux of pure water was observed to increase with an increase in iron oxide content. The permeate flux and rejection rate of sodium alginate (SA) were determined to predict the antifouling behaviour of the membrane. A maximum removal of 90 and 88% of SA was achieved for membranes with a 10 and 1% iron oxide content , respectively, after 3 h. A minor decline in the permeate flux was observed for all membranes after 4 h of operation.

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A novel approach was used to synthesize a silver doped-CNT membrane, with the aim of fully utiliz... more A novel approach was used to synthesize a silver doped-CNT membrane, with the aim of fully utilizing the anti-toxic properties of CNTs and silver. No binder was used for the synthesis of the membrane; instead, silver particles served as a binding material for the CNTs after sintering at high temperature. In the first step, CNTs were impregnated with different loadings of silver (1, 10 and 20 wt.%) via a wet chemistry technique. Impregnated CNTs were then compacted at 200 MPa and sintered at 800 °C for 3 h to form a compact disk (membrane). The powder materials were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray dif-fraction and thermogravimetric analysis, while the membranes were characterized by measuring their porosity, contact angle, diametrical compression test, pure water permeate flux and antibacterial properties. The affinity of the membranes to biofouling was studied using Escherichia coli (E. coli). The produced membrane showed a high water permeate flux and exhibited strong antibacterial properties. All of the membranes with different silver loadings were able to remove/kill 100% of the bacteria tested; however, the CNT membrane with 10% silver showed a superior performance to the others. All bacteria were removed/killed by the membrane with 10% silver loading after the suspension had passed for only 60 min. These membranes would be advantageous in a continuous filtration system for the removal of different contaminants from water via desalination, adsorption and sieving.

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This work reports a comprehensive study of the adsorption characteristics of cadmium(II) on modif... more This work reports a comprehensive study of the adsorption characteristics of cadmium(II) on modified structures of carbon nanotubes (CNTs), carbon nanofibres (CNFs), activated carbon (AC), and fly ash (FA). The characterization was performed using field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface analysis. Several experimental parameters; ad-sorbent dosage, pH, and agitation speed and contact time, were investigated for their effects on the adsorp-tion of cadmium(II) from water. The optimum conditions of 2 h of contact time, pH 7, 50 mg adsorbent dosage and 150 rpm rotational speed were observed. Models of first-order, second-order and pseudo-second-order were fitted to the experimental data, and pseudo-second-order kinetics were observed to describe the adsorption of cadmium(II) on these adsorbents. The adsorption behaviours of cadmium(II) were evaluated using the Freundlich and Langmuir isotherm models. The maximum adsorption capacities of the modified adsorbents were observed to be 2.02 mg/g, 1.98 mg/g, 1.22 mg/g and 1.58 mg/g, for CNTs, AC, CNFs and FA, as obtained from Langmuir isotherm models. It was determined that surface modification of the CNTs, CNFs, and AC enhanced their adsorption efficiency. The results obtained are promising for the use of these modified materials with respect to water purification applications.

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The present study addresses the application of raw and modified carbon nanotubes (CNTs) and activ... more The present study addresses the application of raw and modified carbon nanotubes (CNTs)
and activated carbon (AC) for the removal of hexavalent chromium (Cr(VI)) from aqueous
solution. Surfaces of both the adsorbents were modified by acid treatment. Nitric acid was
used to remove impurities and to introduce carboxylic functional groups on the surfaces of
CNTs and AC. Raw and modified adsorbents (CNTs and AC) were characterized by scanning
electron microscopy, Brunauer–Emmett–Teller surface area analysis, and thermogravimetric
analysis. The influence of adsorbent dosage, contact time, agitation speed, and solution pH
were evaluated on the Cr(VI) removal efficiency using batch adsorption experiments. The
optimum pH for maximum adsorption of Cr(VI) was found to be 3 and 4 for AC and CNTs,
respectively. Modified and raw AC were able to remove 99 and 92% of Cr(VI) ions, respectively,
at 75 mg adsorbent dosage, agitation speed of 200 rpm, initial Cr(VI) concentration of
1 mg/L, contact time of 4 h, and solution pH 3, while the removal of Cr(VI) ions recorded
maximum values of 87 and 80% for modified and raw CNTs under same treatment conditions.
However, acid modification of CNTs was found to have no major effect on the percentage
removal of Cr(VI) ions at low adsorbent dosage. Adsorption capacities of both the adsorbents
were determined using batch adsorption experiments and experimental data were described
by Langmuir and Freundlich adsorption isotherm models. However, Langmuir isotherm
model was able to best describe the adsorption of Cr(VI) ions on raw and modified forms of
CNTs and AC. Maximum adsorption capacity (qe) was found to be 2.024 and 1.805 mg/g for
raw and modified AC, while 1.021 and 0.964 mg/g for raw and modified CNTs.

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