Effect of nickel ion doping in MnO2/reduced graphene oxide nanocomposites for lithium adsorption and recovery from aqueous media

Novel and effective reduced graphene oxide–nickel (Ni) doped manganese oxide (RGO/Ni-MnO₂) adsorbents were fabricated via a hydrothermal approach. The reduction of graphite to graphene oxide (GO), formation of α-MnO₂, and decoration of Ni-MnO₂ onto the surface of reduced graphene oxide (RGO) were independently carried out by a hydrothermal technique. The physical and morphological properties of the as-synthesized adsorbents were analyzed. Batch adsorption experiments were performed to identify the lithium uptake capacities of adsorbents. The optimized parameters for Li⁺ adsorption investigated were pH = 12, dose loading = 0.1 g, Li⁺ initial concentration = 50 mg L⁻¹, in 10 h at 25 °C. It is noticeable that the highest adsorption of Li⁺ at optimized parameters are in the following order: RGO/Ni3-MnO₂ (63 mg g⁻¹) > RGO/Ni2-MnO₂ (56 mg g⁻¹) > RGO/Ni1-MnO₂ (52 mg g⁻¹). A Kinetic study revealed that the experimental data were best designated pseudo-second order for each adsorbent. Li⁺ desorption experiments were performed using HCl as an extracting agent. Furthermore, all adsorbents exhibit efficient regeneration ability and to some extent satisfying selectivity for Li⁺ recovery. Briefly, it can be concluded that among the fabricated adsorbents, the RGO/Ni3-MnO₂ exhibited the greatest potential for Li⁺ uptake from aqueous solutions as compared to others.

Novel and effective reduced graphene oxide–nickel (Ni) doped manganese oxide (RGO/Ni-MnO₂) adsorbents were fabricated via a hydrothermal approach for lithium adsorption and recovery from aqueous media.     

Three-dimensional mesoporous calcium carbonate–silica frameworks thermally activated from porous fossil bryophyte: adsorption studies for heavy metal uptake

In this paper, three-dimensional mesoporous calcium carbonate–silica frameworks have been created from the straw tufa (ST) originating from porous fossil bryophyte by a thermal activation technique. A batch of adsorption kinetic and thermodynamic experiments were used to investigate the adsorption capacity of Cd(ii) onto the samples. The ST after thermal activation has shown a significant ability for the uptake of heavy metals. It exhibited maximum adsorption capacities of 12.76 mg g⁻¹, 14.09 mg g⁻¹, 17.00 mg g⁻¹, and 33.81 mg g⁻¹ for Cd(ii) at the activation temperature of 300, 450, 600 and 750 °C, respectively. Through competitive adsorption for Cd(ii)and Pb(ii), the ST thermally activated at 750 °C exhibited maximum equilibrium adsorption capacities of 24.65 mg g⁻¹, 25.91 mg g⁻¹, and 30.94 mg g⁻¹ for Cd(ii) uptake at 298.1 K, 308.1 K and 318.1 K, respectively, whereas it exhibited values of 91.59 mg g⁻¹, 101.32 mg g⁻¹, and 112.19 mg g⁻¹ for Pb(ii) removal. The adsorption capacities of Cd(ii) and Pb(ii) both decrease with the addition of the other heavy metal cations, indicating that the adsorption is hindered by the competitive adsorption and the adsorption active sites on the mineral surface are readily exchangeable. The adsorption of Cd(ii) and Pb(ii) followed the pseudo-second order kinetics model well. In addition, the Langmuir model could accurately describe the adsorption isotherms. Based on the results of characterization with TEM, XRD and XPS, the adsorption mechanisms could be primarily explained as formation of Cd(OH)₂ and CdCO₃ as well as Cd(HCO₃)₂ precipitation on the surface of ST. These characteristics of ion-exchange and the adsorptive property for ST modified allow it to be widely used in artificial wetland landfill and environmental protection.

Three-dimensional mesoporous calcium carbonate–silica frameworks have been created and have shown excellent adsorption capacities for Cd(ii) and Pb(ii).     

Enhancing adsorption capacity and structural stability of Li1.6Mn1.6O4 adsorbents by anion/cation co-doping

Modifying the structure of Li_1.6Mn_1.6O₄ (LMO) to enhance its structural stability and adsorption capacity is an effective method to generate materials to recover Li⁺ ions from mixed solution. Herein, the co-doping of trace non-metal ion (S) and metal ion (Al) into Li_1.6Mn_1.6O₄ (LMO-SAl) is established and shows excellent Li⁺ adsorption capacity and Mn anti-dissolution properties. The adsorption capacity (when [Li⁺] is 6 mmol L⁻¹) is increased from 26.1 mg g⁻¹ to 33.7 mg g⁻¹. This is attributed to improved charge density via substitution of S at O sites, which facilitates the adsorption/desorption process. The Mn dissolution is also reduced from 5.4% to 3.0% for LMO-SAl, which may result from the stronger Al–O bonds compared to Li–O bonds that enhance the structural stability of the LMO. The ion-sieving ability of the co-doped material goes by the order of K_d (Li⁺ > Ca²⁺ > Mg²⁺ > Na⁺ > K⁺), indicating that Li⁺ can be efficiently separated from Lagoco Salt Lake brine. These results predict that lithium ions are effectively adsorbed from brine by the co-doped LMO material, which manifests the feasibility of lithium recovery and provides basic data for further industrial applications of adsorption.

Modifying the structure of Li_1.6Mn_1.6O₄ (LMO) to enhance its structural stability and adsorption capacity is an effective method to generate materials to recover Li⁺ ions from mixed solution.     

Al-doped H2TiO3 ion sieve with enhanced Li+ adsorption performance

H₂TiO₃ (HTO) is considered to be one of the most promising adsorbents for lithium recovery from aqueous lithium resources duo to its highest theoretical adsorption capacity. However, its actual adsorption capacity is much lower owing to its unknown structure and incomplete leaching of lithium. After Al is doped into H₂TiO₃ (HTO-Al), the adsorption capacity of HTO-Al is 32.12 mg g⁻¹ and the dissolution of Ti is 2.53%. HTO-Al has good adsorption selectivity, and all the separation factors α are ≫1. Furthermore, HTO-Al also exhibits good cyclic stability and solubility resistance. After 5 cycles, the adsorption capacity remains 29.3 mg g⁻¹ and the dissolution rate is 1.7%. Therefore, HTO-Al has potential application value for recovering Li⁺ from aqueous lithium resources.

H₂TiO₃ (HTO) is considered to be one of the most promising adsorbents for lithium recovery from aqueous lithium resources duo to its highest theoretical adsorption capacity.     

Biomass derived hierarchical porous carbon for high-performance O2/N2 adsorption; a new green self-activation approach

Biomass-derived porous carbons are the most common adsorbent materials for O₂/N₂ adsorption because of their excellent textural properties, high surface area, and low expense. A new synthesis method based on a self-activation technique was developed for a new green porous carbon adsorbent. This ecofriendly system was used for the synthesis of hierarchical porous carbons from walnut-shell precursors. The sorbent was successfully synthesized by facile one-step carbonization, with the activating reagents being gases released during the activation. The sample morphology and structure were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray powder diffraction, thermogravimetric, and differential thermal analysis. The optimal porous carbons were synthesized at 1000 °C, providing a surface area as high as 2042.4 (m² g⁻¹) and micropore volume of about 0.499 (m³ g⁻¹). At 298 °K under 9.5 bar pressure, the potential for O₂/N₂ separation using porous carbon samples was studied, and the sips isotherms with the highest adsorption potential were determined to be 2.94 (mmol g⁻¹) and 2.67 (mmol g⁻¹), respectively. The sample exhibited stable O₂/N₂ separation over ten cycles, showing high reusability for air separation. Finally, the technology described presents a promising strategy for producing eco-friendly porous carbon from a variety of biomass on an industrial scale.

Green porous carbon was synthesized by self-activation methodology with facile one-step carbonization from a walnut-shell precursor for air separation. The adsorption process behavior was surveyed using isotherm, kinetic and thermodynamic models.     

Single-walled carbon nanotubes/lithium borohydride composites for hydrogen storage: role of in situ formed LiB(OH)4, Li2CO3 and LiBO2 by oxidation and nitrogen annealing

Lithium Borohydride (LiBH₄), from the family of complex hydrides has received much attention as a potential hydrogen storage material due to its high hydrogen energy densities in terms of weight (18.5 wt%) and volume (121 kg H₂ per mol). However, utilization of LiBH₄ as a hydrogen carrier in off- or on-board applications is hindered by its unfavorable thermodynamics and low stability in air. In this study, we have synthesized an air stable SWCNT@LiBH₄ composite using a facile ultrasonication assisted impregnation method followed by oxidation at 300 °C under ambient conditions (SWLiB-A). Further, part of the oxidized sample is treated at 500 °C under nitrogen atmosphere (SWLiB-N). Upon oxidation in air, the in situ formation of lithium borate hydroxide (LiB(OH)₄) and lithium carbonate (Li₂CO₃) on the surface of the composite (SWLiB@LiBH₄) is observed. But in the case of SWLiB-N, the surface hydroxyl groups [OH₄]⁻ completely vanished leaving porous LiBH₄ with SWCNT, LiBO₂ and Li₂CO₃ phases. Hydrogen adsorption/desorption experiments carried out at 100 °C under 5 bar H₂ pressure showed the highest hydrogen adsorption capacity of 4.0 wt% for SWLiB-A and 4.3 wt% for SWLiB-N composites in the desorption temperature range of 153–368 °C and 108–433 °C respectively. The observed storage capacity of SWLiB-A is due to the H⁺ and H⁻ coupling between in situ formed Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ and Li⁺[BH₄]⁻. Whereas in SWLiB-N, the presence of positively charged Li and B atoms and LiBO₂ acts as a catalyst which resulted in reduced de-hydrogenation temperature (108 °C) as compared to bulk LiBH₄. Moreover, it is inferred that the formation of intermediate phases such as Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ (SWLiB-A) and Li⁺[BO₂]⁻ (SWLiB-N) on the surface of the composites not only stabilizes the composite under ambient conditions but also resulted in enhanced de- and re-hydrogenation kinetics through catalytic effects. Further, these intermediates also act as a barrier for the loss of boron and lithium through diborane release from the composites upon dehydrogenation. Furthermore, the role of in situ formed intermediates such as LiB(OH)₄, Li₂CO₃ and LiBO₂ on the stability of the composite under ambient conditions and the hydrogen storage properties of the SWCNT@LiBH₄ composite are reported for the first time.

In situ formed Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ & Li⁺[BO₂]⁻ on the surface of SWCNT@LiBH₄ not only stabilizes the composites in ambient conditions but also enhanced the de- and re-hydrogenation kinetics of the composites through catalytic effect.     

Three hierarchical porous magnesium borate microspheres: a serial preparation strategy,growth mechanism and excellent adsorption behavior for Congo red

The 3D hierarchical porous 7MgO·2B₂O₃·7H₂O (MBH) microspheres were prepared by a phase transformation of chloropinnoite firstly, and anhydrous α-3MgO·B₂O₃ (MBA) microspheres were obtained by thermal conversion of 7MgO·2B₂O₃·7H₂O, and then β-3MgO·B₂O₃ (MBB) microspheres were obtained by phase conversion of α-3MgO·B₂O₃. All samples were characterized by XRD, FT-IR, TG and SEM. The microsphere nanostructures with a hierarchical porous structure were assembled by nanosheets with a thickness of 20–30 nm, and the growth mechanisms were also proposed. By using N₂ adsorption–desorption, the specific surface areas were measured as 103.62 m² g⁻¹ for MBH and 46.10 m² g⁻¹ for MBA. They exhibited excellent selective adsorption performance for Congo red (CR) with maximum adsorption capacities of 202.84 and 170.07 mg g⁻¹ respectively, and the corresponding adsorption mechanisms were also investigated. The adsorption processes were well fitted with the pseudo-second-order rate equation and Langmuir adsorption model. In addition, the corresponding adsorption thermodynamic parameters were also calculated. It is necessary to highlight that the hierarchical porous microspheres could be considered as promising candidates for removal of CR dye pollutants.

Three 3D hierarchical porous 7MgO·2B₂O₃·7H₂O and 3MgO·B₂O₃ microspheres assembled by nanosheets have been prepared by a serial preparation strategy. They exhibited excellent selective adsorption performance for Congo red with high adsorption capacities.     

Multi-functional porous organic polymers for highly-efficient solid-phase extraction of β-agonists and β-blockers in milk

A simple, accurate, and highly sensitive analytical method was developed in this study for the determination of ten β-agonists and five β-blockers in milk. In this method, new adsorbent phosphonic acid-functionalized porous organic polymers were synthesized through a direct knitting method. The synthesis procedure of the materials and the extraction conditions (such as the composition of loading buffer and eluent) were optimized. Benefitting from the high surface area (545–804 m² g⁻¹), multiple functional framework and good porosity, the phosphonic acid-functionalized porous organic polymers showed a high adsorption rate and high adsorption capacity for β-agonists (224 mg g⁻¹ and 171 mg g⁻¹ for clenbuterol and ractopamine, respectively). The analytes were quantified by ultra-high-performance liquid chromatography coupled to high-resolution tandem mass spectrometry. It showed a good linearity (with R² ranging from 0.9950 to 0.9991 in the linear range of 3–5 orders of magnitude), with low limits of quantification ranging from 0.05 to 0.25 ng g⁻¹. The limits of detection of the method for the analytes were measured to be in the range of 0.02 to 0.1 ng g⁻¹. The recoveries of target analytes from real samples on the material were in the range of 62.4–119.4% with relative standard deviations of 0.6–12.1% (n = 4). Moreover, good reproducibility of the method was obtained with the interday RSD being lower than 11.7% (n = 5) and intraday RSD lower than 12.2% (n = 4). The proposed method was accurate, reliable and convenient for the simultaneous analysis of multiple β-agonists and β-blockers. Finally, the method was successfully applied for the analysis of such compounds in milk samples.

Novel phosphonic acid-functionalized porous organic polymers were synthesized through direct knitting method. It shows high adsorption efficiency and high adsorption capacity for multiple β-agonists and β-blockers analysis.     

Remarkable adsorptive removal of nitrogen-containing compounds from hydrotreated fuel by molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol nanofibers

Molecularly imprinted polymer (MIP) nanofibers were prepared by the electrospinning of poly 2-(1H-imidazol-2-yl)-4-phenol (PIMH) in the presence of various nitrogen containing compounds (N-compounds). Molecularly imprinted polymer nanofibers show selectivity for various target model nitrogen-containing compounds with adsorption capacities of 11.7 ± 0.9 mg g⁻¹, 11.9 ± 0.8 mg g⁻¹ and 11.3 ± 1.1 mg g⁻¹ for quinoline, pyrimidine and carbazole, respectively. Molecular modelling based upon density functional theory (DFT) indicated that hydrogen bond interactions may take place between the lone-pair nitrogen atom of model compounds (quinoline and pyrimidine) and the –OH and –NH groups of the PIMH nanofibers. The adsorption mode followed the Freundlich (multi-layered) adsorption isotherm, which indicated possible nitrogen–nitrogen compound interactions. Molecularly imprinted polymer nanofibers show potential for the removal of nitrogen-containing compounds in fuel.

Molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol nanofibers fabricated via electrospinning displayed excellent selectivity adsorption capacities nitrogen containing compounds (N-compounds) in hydro-treated fuels.     

Biosorption of anionic and cationic dyes via raw and chitosan oligosaccharide-modified Huai Flos Chrysanthemum at different temperatures

Raw Huai Flos Chrysanthemum (HFC) and modified HFC (HFC@CO) were used for the first time as a biosorbent material to remove cationic dyes Malachite green (MG) and Crystal violet (CV), and anionic dyes Sunset yellow (SY), Lemon yellow (LY), and Carmine (CM), at different temperatures (5–50 °C). The highest removal rates (R) for dye adsorption were observed at low temperature (5 °C) and room temperature (20 °C). At high (500 mg L⁻¹) dye concentration, adsorption was completed within one minute, but the time required to reach adsorption equilibrium was longer than at the low (20 mg L⁻¹) concentration. The experimental data fitted very well to the Langmuir model and the values of the maximum adsorption capacity for SY, LY, CM, CV, and MG, were 481.41, 507.23, 141.78 mg g⁻¹, 526.32, and 769.23 mg L⁻¹, respectively. The adsorption data fit well to a pseudo-second-order kinetic model.

Raw Huai Flos Chrysanthemum and modified HFC were used for the first time as a biosorbent to remove cationic dyes Malachite green and Crystal violet, and anionic dyes Sunset yellow, Lemon yellow, and Carmine, at different temperatures (5–50 °C).     

Comparative study of pyrolytic carbons prepared from printed circuit boards by magnetic and electrostatic separation

Physical technology is the main method to separate metal and non-metallic fractions from printed circuit boards (PCBs). The non-metallic fractions from magnetic and electrostatic separation have different ingredients, which enables them to be prepared into pyrolytic carbon with different properties. To discover the influence of separation technologies for PCBs on the preparation, characterization and application of pyrolytic carbon, two kinds of nonmetal fraction from magnetic and electrostatic separation were chosen as the precursors of pyrolytic carbon. The thermogravimetric analysis of non-magnetic fraction and non-conductive fraction at different heating rates was discussed in the paper. The optimal heating rate of 10 °C min⁻¹ was applied in preparing pyrolytic carbons. Pyrolytic carbons prepared from the non-magnetic fraction and non-conductive fraction had visible differences in their morphological and pore structures. Pyrolytic carbons of the non-magnetic fraction exhibited higher BET surface area (313 m² g⁻¹) and higher adsorption capacities for ciprofloxacin (142.82 mg g⁻¹) than those of pyrolytic carbon of the non-conductive fraction (S_BET: 235 m² g⁻¹, q_m: 78.17 mg g⁻¹). Equilibrium data fit better to the Freundlich model than the Langmuir model. According to the calculated thermodynamic parameters, CIP adsorption processes by the two pyrolytic carbons were spontaneous and endothermic. Although the metal recovery from PCBs through electrostatic separation is higher, pyrolytic carbon prepared from the non-magnetic fraction shows better pore characteristics and adsorption properties. This paper might be the first report of the effect of separation technology for PCBs on the preparation of pyrolytic carbons. This paper contributed to the reutilization of non-metallic fractions of PCBs and the development of a cyclic economy.

To discover the influence of separation technologies for PCBs on the preparation, characterization and application of pyrolytic carbon, two kinds of nonmetal fraction from magnetic and electrostatic separation were chosen as the precursors.     

Synthesis,structural characterization and Cu(ii) adsorption behavior of manganite (γ-MnOOH) nanorods

New alternatives for the removal of transition metal ions that present an environmental risk are required. The chemical adsorption of these ions on surfaces with chemisorbent properties represents a promising area of research. In this work, manganite (γ-MnOOH) nanorods were synthesized, with a surface area of 20.22 m² g⁻¹, pore size of 32.18 nm and pore volume of 0.1627 cm³ g⁻¹. After chemical and structural characterization of the manganite sample, it was evaluated as an adsorbent of Cu(ii) from aqueous solution. The equilibrium adsorption data were well fitted by the Langmuir isotherm, and the results indicated that the maximum adsorption capacity of Cu(ii) was 11.926 mg g⁻¹. Cu(ii) ion adsorption on the manganite surface is a spontaneous and exothermic process (ΔG°< 0 and ΔH°< 0). The negative value of ΔS° suggests the stability of the adsorption process without structural change at the manganite–aqueous solution interface. A scheme for chemisorption of Cu(ii) ions on the hydroxylated surface of manganite is proposed.

Manganite (γ-MnOOH) nanorods were synthesized and Cu(ii) adsorption on their hydroxylated surface was a spontaneous process (ΔG° < 0).     

Removal of methylene blue dye using nano zerovalent iron,nanoclay and iron impregnated nanoclay – a comparative study

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry. The sorption process is one conventionally used method. In this study, nanoclay, nano zero valent iron (nZVI), and iron impregnated nanoclay were prepared and studied for the removal of MB dye in batch mode. The effects of operating parameters like pH, dye concentration, sorbent dosage, and contact time were investigated and optimized. The nZVI, nanoclay, and iron impregnated nanoclay sorbents showed zeta potentials of −32.1, −53.4, and −40.7 mV, respectively. All the nano adsorbents were crystalline. The nanoclay was characterized by an average surface area, pore volume and pore diameter of 43.49 m² g⁻¹, 0.104 cm³ g⁻¹ and 2.806 nm, respectively. nZVI showed a surface area of 47.125 m² g⁻¹, pore volume of 0.119 cm³ g⁻¹, and pore diameter of 3.291 nm. And iron impregnated nanoclay showed a surface area of 73.110 m² g⁻¹ with a pore volume of 15 cm³ g⁻¹ and a pore diameter size of 3.83 nm. A Langmuir EXT nitrogen gas adsorption isotherm (R² ∼ 0.99) was the best fit. The thermodynamics parameters, such as ΔG° (−12.64 to −0.63 kJ mol⁻¹), ΔH° (+0.1 to +62.15 kJ mol⁻¹) and ΔS° (+0.10 to +0.22 kJ mol⁻¹), confirmed that a spontaneous and endothermic adsorption process took place at a high rate of disorder. Iron impregnated nanoclay showed higher negative Gibbs free energy (−12.64 kJ mol⁻¹), higher enthalpy change (+62.5 kJ mol⁻¹) and entropy (+0.22 kJ mol⁻¹) and gave a better MB removal performance. In addition, the lower negative heat of enthalpy for all adsorptions proved the dominance of physisorption. The methylene blue adsorption isotherm on nZVI and nanoclay showed the best fit with the Freundlich isotherm model with correlation coefficients (R²) ∼0.98 and 0.99, respectively. Whereas the Langmuir adsorption isotherm was the best fit for iron impregnated nanoclay (R² ∼ 0.98). The adsorption activities of nZVI, nanoclay and iron impregnated nanoclay were fitted to a pseudo-second-order kinetic model with correlation coefficients (R²) of 0.999, 0.997 and 0.983, respectively. The optimal pH 7.0 (RE: 99.1 ± 0.73%), initial MB concentration 40 ppm (RE: 99.9 ± 0.03%), contact time 120 min (RE: 99.9 ± 0.9%), and adsorbent dose 80 (99.9 ± 0.03%) were obtained for iron impregnated nanoclay. The optimal operational parameters of nanoclay and nZVI, respectively, were pH 11.0 and 13.0, initial MB concentration 20 and 20 ppm, adsorbent dose 100 and 140 mg, and contact time 120 and 140 min. In general, iron impregnated nanoclay has shown promising cationic dye adsorbance for industrial applications; but a recyclability test is suggested before scale-up.

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry.     

Bioresource derived porous carbon from cottonseed hull for removal of triclosan and electrochemical application

Biomass-derived porous carbon materials have drawn considerable attention due to their natural abundance and low cost. In this work, nitrogen enriched porous carbons (NRPCs) with large surface areas were designed and prepared from cottonseed hull via simultaneous carbonization and activation with a facile one-pot approach. The NRPCs were tunable in terms of pore structure, nitrogen content and morphology by adjusting the ratio of the carbon precursor (cottonseed hull), nitrogen source (urea), and activation agent (KOH). The as-synthesized NRPCs exhibited three-dimensional oriented and interlinked porous structure, high specific surface area (1160–2573 m² g⁻¹) and a high level of nitrogen-doping (6.02–10.7%). In a three electrode system, NRPCs prepared at 800 °C with the ratio (cottonseed hull : KOH : urea) of 1 : 1 : 2 (NRPC-112) showed a high specific capacitance of 340 F g⁻¹ at a current density of 0.5 A g⁻¹ and good rate capability (∼80% retention at a current density of 10 A g⁻¹) with 6 M KOH as electrolyte. In a two electrode cell, NRPC-112 demonstrated a high specific capacitance of 304 F g⁻¹ at 0.5 A g⁻¹ and an excellent rate capacity (∼71% retention at current density of 10 A g⁻¹) as well as excellent cycling stability (∼91% retention at 5 A g⁻¹) after 5000 cycles. Furthermore, the NRPCs exhibited an extraordinary adsorption capacity up to 205 mg g⁻¹ for emerging pollutant triclosan. The work provided a sustainable approach to prepare functional carbon materials from biomass-based resource for environment remediation and electrochemical applications.

Biomass derived nitrogen-enriched porous carbon materials from cottonseed hull for emerging pollutant triclosan removal and electrochemical application.     

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries

While Li₂MnO₃ as an over-lithiated layered oxide (OLO) shows a significantly high reversible capacity of 250 mA h g⁻¹ in lithium-ion batteries (LIBs), it has critical issues of poor cycling performance and deteriorated high rate performance. In this study, modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO at different temperatures (400, 500, and 600 °C) in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere. Compared to the as-prepared OLO, the OLO sample heated at 500 °C with PVP exhibited a high initial discharge capacity of 206 mA h g⁻¹ and high rate capability of 111 mA h g⁻¹ at 100 mA g⁻¹. The superior performance of the OLO sample heated at 500 °C with PVP is attributed to an improved electronic conductivity and Li⁺ ionic motion, resulting from the formation of the graphitic carbon structure and increased Mn³⁺ ratio during the decomposition of PVP.

The modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere.     

The design of a multifunctional separator regulating the lithium ion flux for advanced lithium-ion batteries

Herein, we design a controllable approach for preparing multifunctional polybenzimidazole porous membranes with superior fire-resistance, excellent thermo-stability, and high wettability. Specifically, the recyclable imidazole is firstly utilized as the eco-friendly template for micropores formation, which is an interesting finding and has tremendous potential for low-cost industrial production. The unique backbone structure of the as-prepared polybenzimidazole porous membrane endows the separator with superb thermal dimensional stability at 300 °C. Most significantly, the inherent flame retardancy of polybenzimidazole can ensure the high security of lithium-ion batteries, and the existence of polar groups of imidazole can regulate the Li⁺ flux and improve the ionic conductivity of lithium ions. Notably, the cell with a polybenzimidazole porous membrane presents higher capability (131.7 mA h g⁻¹) than that of a commercial Celgard membrane (95.4 mA h g⁻¹) at higher charge–discharge density (5C), and it can work normally at 120 °C. The fascinating comprehensive properties of the polybenzimidazole porous membrane with excellent thermal-stability, satisfying wettability, superb flame retardancy and good electrochemical performance indicate its promising application for high-safety and high-performance lithium-ion batteries.

A multifunctional PBI porous membrane with superior fire-resistance, excellent thermo-stability and high wettability is designed.     

Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment

An effective adsorbent of methylene blue was synthesized from coal fly ash (FA; waste material from a coal power plant) by a denaturing process with an alkaline solution at 90 °C. The denatured fly ash (D-FA) has a surface area and pore volume of 66.39 m² g⁻¹ and 15.33 cm³ g⁻¹, respectively, whereas the values of the original FA are negligible, i.e., 3.55 m² g⁻¹ and 0.02 cm³ g⁻¹. The removal of methylene blue (MB) in aqueous solution by D-FA was increased in the range of initial MB concentration (10–20 mg L⁻¹); contact time (0–120 min); pH (2–8); D-FA dosage (1–4 g L⁻¹). However, a larger value of those operational parameters would not improve the removal activity. Furthermore, the methylene blue adsorption on the denatured FA was fitted with the Langmuir model with R² = 0.9991; the maximum adsorption capacity was determined as 28.65 mg g⁻¹ from the model. Overall, the highest removal efficiency of MB using D-FA with the dosage of 4 g L⁻¹ was 97.1% in 30 mg L⁻¹ solution of methylene blue at pH = 7. The alkaline hydrothermal denaturation of waste FA is a promising approach to produce an adsorbent with beneficial environmental engineering applications.

High efficiency of methylene blue adsorbent from waste coal fly ash by treatment with alkaline thermal hydrolysis.     

Enhanced ionic conductivity in halloysite nanotube-poly(vinylidene fluoride) electrolytes for solid-state lithium-ion batteries

Solid composite electrolytes have gained increased attention, thanks to the improved safety, the prolonged service life, and the effective suppression on the lithium dendrites. However, a low ionic conductivity (<10⁻⁵ S cm⁻¹) of solid composite electrolytes at room temperature needs to be greatly enhanced. In this work, we employ natural halloysite nanotubes (HNTs) and poly(vinylidene fluoride) (PVDF) to fabricate composite polymer electrolytes (CPEs). CPE-5 (HNTs 5 wt%) shows an ionic conductivity of ∼3.5 × 10⁻⁴ S cm⁻¹, which is ∼10 times higher than the CPE-0 (without the addition of HNTs) at 30 °C. The greatly increased ionic conductivity is attributed to the negatively-charged outer surface and a high specific surface area of HNTs, which facilitates the migration of Li⁺ in PVDF. To make a further illustration, a solid-state lithium-ion battery with CPE-5 electrolyte, LiMn₂O₄ cathode and Li metal anode was fabricated. An initial discharge capacity of ∼71.9 mA h g⁻¹ at 30 °C in 1C is obtained, and after 250 cycles, the capacity of 73.5 mA h g⁻¹ is still maintained. This study suggests that a composite polymer electrolyte with high conductivity can be realized by introducing natural HNTs, and can be potentially applied in solid-state lithium-ion batteries.

The special structure of HNTs and the further formation of amorphous PVDF contribute to the enhancement of the Li⁺ transfer.     

Nitrogen doped hierarchical activated carbons derived from polyacrylonitrile fibers for CO2 adsorption and supercapacitor electrodes

Nitrogen doped hierarchical activated carbons with high surface areas and different pore structures are prepared form polyacrylonitrile fibers through KOH activation by two steps. It is found that the specific surface area and porosity of the activated carbons depend strongly on the activation temperatures. The specific surface area increases from 607 m² g⁻¹ to 3797 m² g⁻¹ when the activation temperature increases from 600 °C to 800 °C, and then decreases to 3379 m² g⁻¹ at 900 °C. It shows that the hierarchical activated carbon prepared at a moderate activation temperature of 700 °C exhibits the largest CO₂ capture amount, i.e., 5.25 and 3.63 mmol g⁻¹ at 273 and 298 K, respectively, under the pressure of 1 bar. The excellent CO₂ capture properties are due to the high specific surface area of 2146 m² g⁻¹ and high nitrogen content (5.2 wt%) of the obtained sample. On the other hand, when used as supercapacitor electrodes, the sample with the activation temperature at 800 °C shows the largest specific capacitance of 302 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH aqueous electrolyte, with an excellent rate capability of 231 F g⁻¹ at 10 A g⁻¹. Furthermore, a nearly linear relationship between nitrogen content in the nitrogen doped activated carbons and specific CO₂ uptake as well as the specific capacitance were first established, indicating nitrogen doping was playing key roles in improving CO₂ adsorption and supercapacitor performance. The experimental results indicate that the thus obtained nitrogen doped hierarchical activated carbons are very promising for reducing CO₂ green house gas by adsorption as well as storing energy as utilized in supercapacitors.

Nitrogen doped activated carbons with high surface area up to 3797 m₂ g⁻¹ exhibit specific capacitance of 231 F g⁻¹ at a current density of 10 A g⁻¹.     

Adsorption performance of antimony by modified iron powder

Antimony pollution resulting from industrial production is a great threat to the environment, ecology and the human body. Zero-valent iron powder is low-cost and easy to obtain. Nevertheless, the lower adsorption capacity limits its application when it is used as an adsorbent. In the present study, ball-milling and acid modification were developed to change its surface characteristics and γ-Fe₂O₃, γ-FeOOH and Fe₃O₄ were obtained after treatment, which promoted its adsorption capacity. Compared with the raw iron powder, the adsorption capacities for Sb(iii) and Sb(v) using the modified material were increased from 12.93 mg g⁻¹ and 5.47 mg g⁻¹ to 17.96 mg g⁻¹ and 10.58 mg g⁻¹, respectively. The study showed that the experimental data fitted the Langmuir model and the pseudo-first-order kinetic model better; the adsorption process was monolayer and chemically controlled at pH 5.0 ± 0.2. XPS and FT-IR analysis showed that Fe–O–Sb bonds arose during the adsorption process. The effect of pH on the adsorption capacity was also studied and the pH affected the adsorption of Sb(v) more than the adsorption of Sb(iii). In addition, the modified iron powder presented better efficiency when applied to the removal of low levels of antimony in drinking water. Based on the increase of adsorption capacity and low cost, iron powder should be a promising adsorbent for aqueous antimony removal.

Modified iron powders were obtained by ball-milling and acid modification and the adsorption behavior and mechanism for Sb(iii) and Sb(v) analyzed. The improved adsorption capacity and low cost show the application potential of the modified material.