Xianjia Peng

Adsorption of 1,2-dichlorobenzene from water to carbon nanotubes

Abstract The as-grown CNTs and graphitized CNTs were used as adsorbents to remove 1,2-dichlorobenzene from water. The experiments demonstrate that it takes only 40 min for CNTs to attain equilibrium and the adsorption capacity of as-grown and graphitized CNTs is 30.8 and 28.7 mg/g, respectively, from a 20 mg/l solution. CNTs can be used as adsorbents in a wide pH range of 3–10. Thermodynamic calculations indicate that the adsorption reaction is spontaneous with a high affinity and the adsorption is an endothermic reaction.

Arsenite removal from aqueous solutions by γ-Fe2O3–TiO2 magnetic nanoparticles through simultaneous photocatalytic oxidation and adsorption

A novel Fe-Ti binary oxide magnetic nanoparticles which combined the photocatalytic oxidation property of TiO(2) and the high adsorption capacity and magnetic property of γ-Fe(2)O(3) have been synthesized using a coprecipitation and simultaneous oxidation method. The as-prepared samples were characterized by powder XRD, TEM, TG-DTA, VSM and BET methods. Photocatalytic oxidation of arsenite, the effect of solution pH values and initial As(III) concentration on arsenite removal were investigated in laboratory experiments. Batch experimental results showed that under UV light, As(III) can be efficiently oxidized to As(V) by dissolved O(2) in γ-Fe(2)O(3)-TiO(2) nanoparticle suspensions at various pH values. At the same time, As(V) was effectively removed by adsorption onto the surface of nanoparticles. The maximum removal capability of the nano-material for arsenite was 33.03 mg/g at pH 7.0. Among all the common coexisting ions investigated, phosphate was the greatest competitor with arsenic for adsorptive sites on the nano-material. Regeneration studies verified that the γ-Fe(2)O(3)-TiO(2) nanoparticles, which underwent five successive adsorption-desorption processes, still retained comparable catalysis and adsorption performance, indicating the excellent stability of the nanoparticles. The excellent photocatalytic oxidation performance and high uptake capability of the magnetic nano-material make it potentially attractive material for the removal of As(III) from water.

Removal of phosphate from aqueous solution by red mud using a factorial design.

The purpose of the work is to study the adsorption of phosphate on red mud from aqueous solutions using 2(3) full factorial designs. The important parameters, which affect the removal efficiency of phosphate and final pH of solution (pH(f)), such as phosphate concentration, initial pH of solution (pH(i)) and the red mud dosage were investigated. The effects of individual variables and their interaction effects for dependent variables, namely, phosphate removal efficiency and pH(f) were determined. The results of the study showed that phosphate removal efficiency and pH(f) were found to be 97.6% and 10.9 with optimal reaction conditions initial phosphate concentration 25 mg l(-1), red mud dosage 1.5 g l(-1), pH(i) 3.0, respectively. It was found that adequate amount of calcium ions and higher final pH than 9 are ideal conditions for maximum phosphate removal.

Aqueous stability of oxidized carbon nanotubes and the precipitation by salts.

The stability of nitric acid oxidized carbon nanotubes (CNTs) and the precipitation of oxidized CNTs in water by salts were investigated. Stability investigation shows that during an aging time of 30 days, oxidized CNTs dispersion shows characteristic UV-vis absorbance peak of individual CNTs at 252 nm and CNTs concentration in the dispersion after 30d aging is 85% of the initial concentration. The precipitation value of salts were measured and the precipitation value follows the order of NaCl>KCl>1/2(MgCl(2))>1/2(CaCl(2))>1/3(FeCl(3))>1/3(AlCl(3)). The nature of anions investigated has little effect on precipitation values of salts.

Carbon nanotubes - the promising adsorbent in wastewater treatment

Carbon materials are a class of significant and widely used engineering adsorbent. As a new member of the carbon family, carbon nanotubes have exhibited great potentials in applications as composite reinforcements, field emitters for flat panel display, sensors, energy storage and energy conversion devices, and catalysts support phases, because of their extraordinary mechanical, electrical, thermal and structural properties. In particular, the large specific surface areas, as well as the high chemical and thermal stabilities, make carbon nanotubes an attractive adsorbent in wastewater treatment. The adsorption properties of the carbon nanotubes to a series of toxic agents, such as lead, cadmium and 1, 2-dichlorobenzene have been studied and the results show that carbon nanotubes are excellent and effective adsorbent for eliminating these harmful media in water. The effects of the morphologies and the surface status on the carbon nanotube adsorption capacities are also discussed.

Sorption of endrin to montmorillonite and kaolinite clays

It has been discovered previously that clay minerals may have a greater potential for sorption of pesticides. In this paper, the sorption of endrin, a nonionic persistent organochlorine pesticide, to montmorillonite and kaolinite was investigated. The effect of pH, ionic strength on the sorption was studied. The effect of intercalation of hydroxyl aluminium species on sorption of endrin to montmorillonite was also investigated. The results show that, the sorption isotherm of endrin to montmorillonite and kaolinite was linear. The sorption increases with the increase in ionic strength. pH has effect on the sorption and the sorption on both montmorillonite and kaolinite has obvious troughs at pH about 7.2 and 5.4, respectively. The intercalation of hydroxyl aluminium species decreases the sorption. Sorption mechanism of endrin to montmorillonite and kaolinite was suggested to be a combination of hydrophobic interaction and charge-dipole interaction and troughs in the effect of pH on sorption was attributed to the proton shift reaction of the broken bonds at the clay edges.

Regeneration of carbon nanotubes exhausted with dye reactive red 3BS using microwave irradiation.

Carbon nanotubes (CNTs) exhausted with dye reactive red 3BS were regenerated by microwave irradiation under N(2) atmosphere. High regeneration efficiency was achieved and the regeneration efficiency reached 92.8% after four cycles regeneration. The decrease in adsorption capacity was suggested to be due to the deposition of decomposition residues in CNT pores, which blocked the carbon porosity and decreased the specific surface area.

Silver nanoparticles decorated anatase TiO2₂nanotubes for removal of pentachlorophenol from water.

One-dimensional nanotubes are promising materials for environmental applications. In this study, anatase TiO2 nanotubes (TNTs) were fabricated using an alkaline hydrothermal method at 130°C and then calcinated at 400°C for 2h. Ag nanoparticles were photo-deposited onto the TNTs for enhanced photodegradation of pentachlorophenol (PCP) under simulated solar light. The samples were characterized using transmission electron microscopy, physical adsorption of nitrogen, X-ray diffraction, X-ray photoelectron spectroscopy and UV-Visible diffuse reflectance spectroscopic techniques. The as-synthesized TNTs showed tubular structures with the outer and inner diameter of 9-10 and 5-6 nm, respectively. The results showed that metallic Ag nanoparticles were uniformly dispersed on the TNTs surface, and Ag/TNTs exhibited significant visible-light absorption. After 180 min irradiation, about 99% PCP was removed by Ag/TNTs (5.4 at.%), compared to 54.3% by P25 and 59.4% by pure TNTs. This is attributed to the synergistic effects between Ag nanoparticles acting as traps to effectively capture the photo-generated electrons, and the localized surface plasmon resonance (LSPR) of Ag nanoparticles promoting the absorption of visible light. The intermediates during the PCP photodegradation were systematically analyzed, ruling out the existence of high toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. Ag/TNTs showed excellent stability even after five cycles.

Preparation of coagulant from red mud and semi-product of polyaluminum chloride for removal of phosphate from water

Abstract Traditionally, calcium aluminate, caustic soda, lime or aluminum slag was employed as alkali for basicity adjustment in the production of polyaluminum chloride (PACl). In this work, red mud (RM), a highly alkaline waste from alumina industry, was utilized instead of the traditional alkali. A composite coagulant (RMPACl) was prepared from RM and the semi-product of polyaluminum chloride (ACl). Important factors for preparation, such as RM/ACl ratio, reaction temperature and reaction time, were investigated and optimized to be as follows: RM/ACl ratio of 0.25 (w v−1), reaction temperature of 80°C and reaction time of 4 h. The results of coagulation tests showed that RMPACl exhibited better performance than PACl for removal of phosphate. The optimum coagulation pH range of RMPACl was found to be 6.0–8.5. High phosphate removal efficiency (>94.9%) was achieved by dosing RMPACl at the dosage of 147.5 mg l−1. Therefore, RMPACl was considered as a low-cost coagulant, which possessed a good coagulation p...

Evaluation of arsenic immobilization in red mud by CO2 or waste acid acidification combined ferrous (Fe2+) treatment

Arsenic was detected in a red mud (RM) produced during alumina production from bauxite known as the Bayer process. The transporting RM was a mixture of RM solid phase (RMsf) and RM liquid phase (RMlf). The mass content of RMsf in RM is about 30-40%. The alkalinities concentrations in the RMlf were in a range of 37.2 × 10(3)mg/l to 51.5 × 10(3)mg/l. Acidification by CO(2) or waste acid (WA) combined with ferrous (Fe(2+)) treatment was evaluated for arsenic immobilization in the RM. The aqueous arsenic concentration in the RMlf decreased from 6.1mg/l to 0.5mg/l and 0.06 mg/l with the addition of CO(2) and WA, respectively. Ferrous was then added to decrease the aqueous arsenic concentration to be lower than 0.05 mg/l. The cost-effective dosages of CO(2) or WA were 80.1g/l or 26.7 g/l, and the corresponding dosages of ferrous were both 6g/l. A 2(3) full factorial design was employed to evaluate the importance of chemical components of the RM in the cost of arsenic immobilization. High concentrations of arsenic and alkalinities in the RM will increase the cost while the effects of alumina contents varied during the different acidifications. Dissolvable arsenic in the RMsf was 8.2% and 9.5% after the CO(2) and WA combined ferrous treatments, respectively.