Luhua Jiang

Biochar as potential sustainable precursors for activated carbon production: Multiple applications in environmental protection and energy storage

There is a growing interest of the scientific community on production of activated carbon using biochar as potential sustainable precursors pyrolyzed from biomass wastes. Physical activation and chemical activation are the main methods applied in the activation process. These methods could have significantly beneficial effects on biochar chemical/physical properties, which make it suitable for multiple applications including water pollution treatment, CO2 capture, and energy storage. The feedstock with different compositions, pyrolysis conditions and activation parameters of biochar have significant influences on the properties of resultant activated carbon. Compared with traditional activated carbon, activated biochar appears to be a new potential cost-effective and environmentally-friendly carbon materials with great application prospect in many fields. This review not only summarizes information from the current analysis of activated biochar and their multiple applications for further optimization and understanding, but also offers new directions for development of activated biochar.

Grafting of β-cyclodextrin to magnetic graphene oxide via ethylenediamine and application for Cr(VI) removal.

A novel β-cyclodextrin (β-CD) polymer adsorbent named β-cyclodextrin/ethylenediamine/magnetic graphene oxide (CD-E-MGO) was synthesized for decontamination of Cr(VI) from aqueous solution. The sorption kinetics, isotherms and thermodynamics, as well as the effects of pH, aniline and ionic strength on the sorption process were investigated. The results indicated that CD-E-MGO could effectively remove Cr(VI) from aqueous solution and the sorption data could be well described by pseudo-second-order and Langmuir models. The intraparticle diffusion study indicated that intraparticle diffusion was not the only rate-limiting step. Thermodynamic parameters revealed that the sorption reaction was an endothermic and spontaneous process. The decontamination of Cr(VI) was influenced by solution pH and ionic strength. In the system with aniline, the Cr(VI) sorption was improved at low pH values but reduced at high pH values. These results are important for estimating and optimizing the removal of metal ions by CD-E-MGO composite.

Investigation of the adsorption-reduction mechanisms of hexavalent chromium by ramie biochars of different pyrolytic temperatures

To investigate the relationship between Cr(VI) adsorption mechanisms and physio-chemical properties of biochar, ramie residues were oxygen-limited pyrolyzed under temperature varying from 300 to 600°C. Batch adsorption experiments indicated that higher pyrolysis temperature limits Cr(VI) sorption in terms of capacity and affinity due to a higher aromatic structure and fewer polar functional groups in biochar. Both electrostatic (physical) and ionic (chemical) interactions were involved in the Cr(VI) removal. For low-temperature biochar, the simple physical adsorption was limited and the significant improvement in Cr(VI) sorption was attributed to abundant carboxyl and hydroxyl groups. The adsorption-reduction mechanisms could be concluded that Cr(VI) ions were electrostatically attracted by the positively charged biochar surface and reduced to Cr(III), and then the converted Cr(III) was retained or discharged into the solution. The study demonstrates ramie residues can be converted into biochar as a low-cost and effective sorbent for Cr(VI) removal.

Bioremediation mechanisms of combined pollution of PAHs and heavy metals by bacteria and fungi: A mini review

In recent years, knowledge in regard to bioremediation of combined pollution of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by bacteria and fungi has been widely developed. This paper reviews the species of bacteria and fungi which can tackle with various types of PAHs and heavy metals entering into environment simultaneously or successively. Microbial activity, pollutants bioavailability and environmental factors (e.g. pH, temperature, low molecular weight organic acids and humic acids) can all affect the bioremediation of PAHs and heavy metals. Moreover, this paper summarizes the remediation mechanisms of PAHs and heavy metals by microbes via elucidating the interaction mechanisms of heavy metals with heavy metals, PAHs/PAHs metabolites with PAHs and PAHs with heavy metals. Based on the above reviews, this paper also discusses the potential research needs for this field.

Adsorption of Estrogen Contaminants by Graphene Nanomaterials under Natural Organic Matter Preloading: Comparison to Carbon Nanotube, Biochar, and Activated Carbon

Adsorption of two estrogen contaminants (17β-estradiol and 17α-ethynyl estradiol) by graphene nanomaterials was investigated and compared to those of a multi-walled carbon nanotube (MWCNT), a single-walled carbon nanotube (SWCNT), two biochars, a powdered activated carbon (PAC), and a granular activate carbon (GAC) in ultrapure water and in the competition of natural organic matter (NOM). Graphene nanomaterials showed comparable or better adsorption ability than carbon nanotubes (CNTs), biochars (BCs), and activated carbon (ACs) under NOM preloading. The competition of NOM decreased the estrogen adsorption by all adsorbents. However, the impact of NOM on the estrogen adsorption was smaller on graphenes than CNTs, BCs, and ACs. Moreover, the hydrophobicity of estrogens also affected the uptake of estrogens. These results suggested that graphene nanomaterials could be used to removal estrogen contaminants from water as an alternative adsorbent. Nevertheless, if transferred to the environment, they would also adsorb estrogen contaminants, leading to great environmental hazards.

Tetracycline absorbed onto nitrilotriacetic acid-functionalized magnetic graphene oxide: Influencing factors and uptake mechanism

A novel magnetic nanomaterial was synthesized by grafting nitrilotriacetic acid to magnetic graphene oxide (NDMGO), which was applied as an adsorbent for removing tetracycline (TC) from aqueous solutions. The nanomaterial was characterized using TG-DTA, SEM, TEM, XRD, VSM, XPS, Raman, BET surface area and zeta potential measurements. Several experimental conditions (solution pH, adsorption time, temperature, ionic strength and foreign ions) affecting the adsorption process were investigated. The results showed that the TC adsorption capacity could be affected by solution pH. The adsorption capacity of TC increased rapidly in the initial 20min and finally reached equilibrium was about 600min. The pseudo-second-order kinetics provided the better correlation for the experiment data. Various thermodynamic parameters indicated that the adsorption was a spontaneous and endothermic process. The presence of NaCl and background electrolytes in the solution had a slight influence on TC adsorption. Hydrogen bonds, amidation reaction, π-π and cation-π interaction between NDMGO and TC could be used to explain the adsorption mechanism. The regeneration experiment demonstrated that this nanomaterial possessed an excellent regeneration performance. Based on the experimental results and comparative analysis with other adsorbents, the NDMGO was a high-efficiency and reusable adsorbent for TC pollution control.

Production of biochars from Ca impregnated ramie biomass (Boehmeria nivea (L.) Gaud.) and their phosphate removal potential

This work explored the efficiency and mechanisms of phosphate (P) removal by Ca-impregnated biochar prepared from CaCl2-pretreated ramie stem (Ca-RSB) and ramie bark (Ca-RBB). The properties of Ca-modified biochar were analyzed using elemental analysis, scanning electron microscopy (SEM), BET specific surface analysis, energy-dispersive X-ray analysis (EDS), Fourier transform infrared (FTIR) and a zeta potential meter. The results of characterization suggested that the Ca-RSB had a much higher H/C ratio, total pore volume, BET surface area and more functional groups compared with pristine biochar (RSB). In addition, a higher yield of Ca-RSB (50.8%) than RSB (28.0%) was also observed. Comparison experiments suggested that Ca-RSB showed higher adsorption capacity than Ca-RBB and the adsorption amount of Ca-RSB was more than two-folds that of RSB. Adsorption experimental data fitted well with pseudo-second order kinetics and the Langmuir isotherm. The intra-particle diffusion and Boyds film-diffusion models revealed that the rate-controlled step was controlled by film-diffusion initially and then followed by intra-particle diffusion. Electrostatic attraction served as the main force to adsorb phosphates at a lower pH, and the precipitation and surface deposition took over at higher pH. The results of this study indicated that Ca-RSB is a potential effective and low-cost adsorbent for phosphate removal from wastewater.

Decontamination of methylene blue from aqueous solution by magnetic chitosan lignosulfonate grafted with graphene oxide: effects of environmental conditions and surfactant

In this study, magnetic chitosan lignosulfonate grafted with graphene oxide (MCLS/GO) as an innovative adsorbent was prepared successfully through a hydrothermal reaction. The adsorbent was also characterized using SEM, XRD, VSM, FTIR, XPS, and zeta-potential. The effects of pH, ionic strength, temperature and SDBS (sodium dodecylbenzene sulfonate) on the adsorption behavior of MB (methylene blue) by the MCLS/GO were investigated. The results indicate that MB removal is found to be more effective at a higher pH value and temperature. The adsorption process could be affected by ionic strength, particularly at a higher concentration. Isotherm and kinetics were well-fitted by a Langmuir isotherm model and pseudo-second-order model, respectively. In addition, the presence of SDBS had a positive effect on MB adsorption onto MCLS/GO. An intra-particle diffusion model indicates that both film diffusion and intra-particle diffusion were the rate-controlling processes. Thermodynamic analysis showed that the adsorption reaction was an endothermic and spontaneous process. The adsorption mechanism was proposed to be electrostatic attraction, π–π stacking interaction and hydrogen bonding via FTIR analysis. In conclusion, this study implies that MCLS/GO nanoparticles could be conveniently separated from a water body by an external magnet and utilized as an efficient adsorbent for environment purification.

Biochar pyrolyzed from MgAl-layered double hydroxides pre-coated ramie biomass (Boehmeria nivea (L.) Gaud.): Characterization and application for crystal violet removal

A novel biochar/MgAl-layered double hydroxides composite (CB-LDH) was prepared for the removal of crystal violet from aqueous solution by pyrolyzing MgAl-LDH pre-coated ramie stem (Boehmeria nivea (L.) Gaud.). Pyrolysis played dual role for both converting biomass into biochar and calcining MgAl-LDH during the pyrolysis process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and zeta potential analysis were used to characterize the CB-LDH. The results of characterization suggested that the calcined LDH was successfully synthesized and coated on biochar. The resulted CB-LDH had higher total pore volume and more functional groups than the pristine biochar. Adsorption experimental data fitted well with the pseudo-second order kinetics model and the Freundlich isotherm model. The rate-controlled step was controlled by film-diffusion initially and then followed by intra-particle diffusion. Thermodynamic analysis showed that the adsorption of crystal violet was a spontaneous and endothermic process. The higher pH and temperature of the solution enhanced the adsorption performance. CB-LDH could also have excellent ability for the removal of crystal violet from the actual industrial wastewater and groundwater with high ionic strength. LDH adsorption, electrostatic attraction, pore-filling, π-π interaction and hydrogen bond might be the main mechanisms for crystal violet adsorption on CB-LDH. The results of this study indicated that CB-LDH is a sustainable and green adsorbent with high performance for crystal violet contaminated wastewater treatment and groundwater remediation.

Synthesis of graphene oxide decorated with core@double-shell nanoparticles and application for Cr(VI) removal

A novel graphene oxide composite, namely Fe3O4@SiO2@ chitosan/GO nanocomposite (MSCG) was synthesized for decontamination of Cr(VI) from aqueous solution. High-resolution transmission electron microscopy revealed a core@double-shell structure of the nanoparticles with iron oxide as the core, silica as the inner shell and chitosan as the outer shell. The characteristic results of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and X-ray diffraction (XRD) showed that the Fe3O4@SiO2@chitosan particles were successfully assembled on the surface of the GO layers. The adsorption kinetics followed the pseudo-second-order model and the novel MSCG adsorbent exhibited better Cr(VI) removal efficiency in solutions at low pH. Thermodynamic parameters revealed that the sorption reaction was endothermic and spontaneous. Moreover, the adsorption capacity was about 90% of the initial saturation adsorption capacity after being used four times. By using a permanent magnet, the recycling process of both the MSCG adsorbents and the adsorbed Cr(VI) is more economically sustainable. These results suggest that MSCG is a potential and suitable candidate for the preconcentration and separation of Cr(VI) from wastewater and for the deep-purification of polluted water.