John Barford

Reactive Black dye adsorption/desorption onto different adsorbents: Effect of salt, surface chemistry, pore size and surface area

The adsorption of a large reactive dye, Reactive Black 5 dye, onto two bamboo based active carbons using phosphoric acid in a two stage activation process and three conventional adsorbents, carbon F400, bone char and peat, has been studied. The monolayer saturation adsorption capacities for Reactive Black 5 were determined by the Langmuir isotherm analysis and are: 176, 157, 7, 447 and 545 mg dye/g adsorbent for active carbon F400, bone char, peat, bamboo carbon (2123 m(2)/g) and bamboo carbon (1400 m(2)/g), respectively. The equilibrium experiments were analysed using three isotherms, Langmuir, Freundlich and Redlich-Peterson and the based on the lowest SSE values, the Redlich-Peterson was the best fit correlation. The effect of adding salt, in the form of sodium phosphate, on the adsorption capacities has been studied and was found to increase the adsorption capacities of both bamboo carbons to over 900 mg/g.

Biofiltration as an odour abatement strategy.

The chemical, physical and biological processes occurring in biofiltration are reviewed. A survey of operating biofilter performances is also presented and includes some novel comparative methods. It is concluded that biofiltration is a simple and cost-effective technology for odour removal and that an understanding of the many interactions occuring within the biofilter is essential for the optimal performance of the biofilter.

Production and comparison of high surface area bamboo derived active carbons.

High surface area activated carbons have been produced from the natural biomaterial bamboo, using phosphoric acid as the activating agent. The effects of phosphoric acid impregnation ratio, activation temperature, heating rate on the carbon surface area, porosity and mass yield are presented. Three of these bamboo derived active carbons, surface areas 1337, 1628 and 2123m(2)/g were assessed for their ability to adsorb Acid Red 18 dye from aqueous solution; these results were compared with three conventional adsorbents: activated carbon F400, bone char and peat. Isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson and Langmuir-Freundlich isotherms. Different isotherms provided the best fit correlations to the adsorption experimental data but the Langmuir-Freundlich equation provided the best overall correlation of data. The adsorption capacities of two of the selected bamboo derived carbons were much greater than the capacities of the other three adsorbents.

Solar photocatalytic thin film cascade reactor for treatment of benzoic acid containing wastewater.

A solar photocatalytic cascade reactor was constructed to study the photocatalytic oxidation of benzoic acid in water under various experimental and weather conditions at HKUST. Nine stainless steel plates coated with TiO(2) catalyst were arranged in a cascade configuration in the reactor. Photolytic degradation and adsorption were confirmed to be insignificant total organic carbon (TOC) removal mechanisms. A turbulent flow pattern and, hence, improved mixing in the liquid film were achieved due to the unique cascade design of the reactor. The photoinduced consumption of oxygen during reactions was demonstrated in a sample experiment. The proposed rate equations provided good fits to 90 data points from 17 experiments. The regression results showed that the TOC removal rates averaged over 30 min intervals did not illustrate significant dependence on TOC(0) and that I(mean) was more important in affecting the photocatalytic process within the ranges of the data examined. The percentage removal of TOC in 7 l of 100 mg/l (or 100 ppm) benzoic acid solutions increased from 30% to 83% by adding 10 ml of hydrogen peroxide solution (30 wt%). Hydrogen peroxide was also shown to enhance the efficiency of the degradation process at elevated temperatures. Ortho-, meta- and para-hydroxybenzoic acids were identified by HPLC analysis as the intermediates of benzoic acid during reactions without the addition of hydrogen peroxide solutions.

Novel application of the nonmetallic fraction of the recycled printed circuit boards as a toxic heavy metal adsorbent

Printed circuit boards (PCBs) constitute one of the major sources of toxicity in landfill areas throughout the world. Hence, PCB recycling and separation of its metallic and nonmetallic components has been considered a major ecological breakthrough. Many studies focus on the metallic fraction of the PCBs due to its economic benefits whereas the nonmetallic powder (NMP) has been left isolated. In this work, the feasibility of using NMP as an adsorbent to remove charged toxic heavy metal ions have been studied and its efficiency has been compared with two widely-used commercial adsorbents. The results indicated that the virgin NMP material has no adsorption capacity, while the application of an activation stage to modify the NMP process has a significant effect on its porosity and thus adsorption capacity. The Cu and Pb removal capacity of the activated sample (A-NMP) at a pH level of 4 was 3 mmol and 3.4 mmol per gram of the adsorbent, respectively, which was considerably higher than the commercial ones.

Toxic Heavy Metal Capture Using a Novel Electronic Waste-Based Material-Mechanism, Modeling and Comparison

In the modern communication era, the disposal of printed circuit boards is ecologically of dire concern on a global scale. The two prevalent methods applied for the disposal of this waste are either incineration or landfilling both of which are viewed with skepticism due to their negative environmental impact. Activation of the nonmetallic fraction of this waste leads to the development of a mesoporous material with highly functional groups which can potentially be applied for heavy metal uptake. The removal of copper, lead, and zinc was studied employing a cost-effective novel adsorbent based on waste printed circuit boards. The results indicate that the modification of the original e-waste material has a considerable effect on its surface area enhancement. Adsorption experiments revealed that the modified novel material had uptake capacities of 2.9 mmol Cu, 3.4 mmol Pb, and 2.0 mmol Zn per each gram of the adsorbent which are significantly higher values than its commercial counterparts used in industry.

A comparative study on selective adsorption of metal ions using aminated adsorbents

It is well-known that chitosan consists of amino groups for the chelation of metal ions while NH2-MCM-41 has excellent adsorption selectivities for metals. This work compares both adsorption capacities and selectivities of chitosan and NH2-MCM-41. It has been found that chitosan has adsorption capacities of 1.76 mmol/g, 1.03 mmol/g and 1.30 mmol/g for Cu2+, Ni2+ and Zn2+ respectively whereas NH-MCM-41 has adsorption capacity of 1.52mmol/g, 0.8mmol/g and 0.83mmol/g for Cu, Ni and Zn. The higher adsorption capacity in chitosan is attributed to its higher loading of amine groups. The single component adsorption isotherms were well-fitted using Freundlich model. The binary adsorptions of Cu2+-Zn2+ and Ni2+-Zn2+ systems showed similar adsorption selectivities for both adsorbents. However, chitosan has no preferential adsorption for Ni2+-Zn2+ system while NH2-MCM-41 has a good selectivity towards Zn2+. It is believed that the difference can be attributed to the heterogeneous surface of chitosan due to its organic nature. The multi-component adsorptions were best described by a multicomponent extended Freundlich model. Despite the surface functional group, this work indicates the importance of the adsorbent support on selective adsorption.

Effect of thermal treatment on the photocatalytic activity of TiO2 coatings for photocatalytic oxidation of benzoic acid

The effects of thermal treatment on the properties and photoactivities of TiO 2 catalysts supported on 316 stainless steel plates were examined. Degussa P-25 was immobilized on 316 stainless steel plates by electrophoretic deposition. These TiO 2 -coated plates were heated at 473, 673, and 873 K for 1 h. The photoactivities of these TiO 2 coatings were determined based on the removal of benzoic acid as the model pollutant. In particular, the photoactivity decreased by 52% in the sample heated at 873 K compared with the unheated sample. The results of x-ray diffraction showed that the crystallinity and the crystallite sizes of the catalysts supported on the plates did not significantly vary with increasing temperature over the range examined. Negligible change in the catalyst phase (the anatase-to-rutile ratio) was indicated from x-ray diffraction and micro-Raman spectroscopy. However, it was found that the Brunauer-Emmett-Teller surface area of the scraped catalysts heated at 873 K decreased by nearly 13% compared with the unheated sample. In addition, scanning electron microscopy/energy dispersive x-ray and x-ray photoelectron spectroscopy analyses also detected the presence of Fe 3 + ions at the surface of the supported catalysts heated at 873 K. The drop in surface area and the presence of Fe 3 + ions at the catalyst surface, which were considered to function as electron-hole recombination centers, were possible factors leading to the drop in the photoactivity exhibited by the sample. A lower temperature for thermal treatment such as 473 K was proposed to ensure the coating stability and the catalyst photoactivity.

Alteration of xylose reductase coenzyme preference to improve ethanol production by Saccharomyces cerevisiae from high xylose concentrations.

A K270R mutation of xylose reductase (XR) was constructed by site-direct mutagenesis. Fermentation results of the F106X and F106KR strains, which carried wild type XR and K270R respectively, were compared using different substrate concentrations (from 55 to 220 g/L). After 72 h, F106X produced less ethanol than xylitol, while F106KR produced ethanol at a constant yield of 0.36 g/g for all xylose concentrations. The xylose consumption rate and ethanol productivity increased with increasing xylose concentrations in F106KR strain. In particular, F106KR produced 77.6g/L ethanol from 220 g/L xylose and converted 100 g/L glucose and 100g/L xylose into 89.0 g/L ethanol in 72h, but the corresponding values of F106X strain are 7.5 and 65.8 g/L. The ethanol yield of F106KR from glucose and xylose was 0.42 g/g, which was 82.3% of the theoretical yield. These results suggest that the F106KR strain is an excellent producer of ethanol from xylose.

Multilayer Dye Adsorption in Activated Carbons—Facile Approach to Exploit Vacant Sites and Interlayer Charge Interaction

Altering the textural properties of activated carbons (ACs) via physicochemical techniques to increase their specific surface area and/or to manipulate their pore size is a common practice to enhance their adsorption capacity. Instead, this study proposes the utilization of the vacant sites remaining unoccupied after dye uptake saturation by removing the steric hindrance and same-charge repulsion phenomena via multilayer adsorption. Herein, it has been shown that the adsorption capacity of the fresh AC is a direct function of the dye molecular size. As the cross-sectional area of the dye molecule increases, the steric hindrance effect exerted on the neighboring adsorbed molecules increases, and the geometrical packing efficiency is constrained. Thus, ACs saturated with larger dye molecules render higher concentrations of vacant adsorption sites which can accommodate an additional layer of dye molecules on the exhausted adsorbent through interlayer attractive forces. The second layer adsorption capacity (60-200 mg·g(-1)) has been demonstrated to have a linear relationship with the uncovered surface area of the exhausted AC, which is, in turn, inversely proportional to the adsorbate molecular size. Unlike the second layer adsorption, the third layer adsorption is a direct function of the charge density of the second layer.