Activated carbons derived from hydrothermal impregnation of sucrose with phosphoric acid: remarkable adsorbents for sulfamethoxazole removal

A series of activated carbons with surface areas of 925–1929 m² g⁻¹ were synthesized by in situ hydrothermal impregnation of sucrose with H₃PO₄ and subsequent calcination at 500–900 °C. The prepared various types of activated carbons were utilized for the removal of sulfamethoxazole (SMX) from its solution by adsorption, and the effects of contact time, adsorbent dosage, initial concentration, adsorption temperature and pH on SMX adsorption were studied. The pseudo-second-order and the intra-particle diffusion model were used to analyze the adsorption kinetic data. The adsorption isotherm studies showed that the activated carbon prepared at 900 °C (C-900) showed the highest Langmuir maximum adsorption capacity of 808.7 mg g⁻¹ among them, much higher than that of C-500 (274.0 mg g⁻¹). Adsorption thermodynamic results showed that the adsorption of SMX was a spontaneous exothermic process, with a standard enthalpy change of −6.59 kJ mol⁻¹ and a standard entropy change of 47.7 J mol⁻¹ K⁻¹. It was deduced that hydrophobic, electron donor–acceptor and electrostatic interactions were involved in the adsorption mechanism. Finally, regeneration experiments showed that more than 90% of the adsorption capacity could be recovered after four cycles through ethanol washing. Considering the remarkable and regenerable adsorption ability as well as the economic and environmental merits, these activated carbons are considered as promising candidates for potential practical applications in adsorptive removal of SMX.

Activated carbons obtained by hydrothermal impregnation of sucrose with H₃PO₄ for highly efficient sulfamethoxazole adsorption.     

Morphology control of α-Fe2O3 towards super electrochemistry performance

α-Fe₂O₃ with various morphologies including spindle, rod, tube, disk, and ring were synthesized through controlling the H₂PO₄⁻ etching process. The concentrations of H₂PO₄⁻ plays an important role in controlling the morphology change of the samples. Selected adsorption of H₂PO₄⁻ ions resulted in anisotropic growth. In addition, the etching of H₂PO₄⁻ occurred in the center of rods which resulted in tubal α-Fe₂O₃. Nanodiscs were created once the etching process occurred on the wall of the tube. The electrochemical test shows that disklike samples revealed excellent specific capacitance, rate capacity and cycling stability because of relative higher surface area and pore structure. For the CO catalytic oxidation properties, spindle samples exhibited super catalytic activity.

α-Fe₂O₃ with various morphologies including spindle, rod, tube, disk, and ring were synthesized through controlling the H₂PO₄⁻ etching process.     

Synthesis of hierarchical MgO based on a cotton template and its adsorption properties for efficient treatment of oilfield wastewater

A biomorphic MgO nanomaterial was fabricated via a facile and low-cost immersion method using cotton as the template. The obtained materials were characterized via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and N₂ adsorption–desorption analysis. The as-prepared MgO retained the structure of cotton, with a porous hierarchical structure and a high specific surface area, which endowed it with great potential due to its excellent adsorption properties for the adsorption of additives in oil field wastewater. It also exhibited the maximum adsorption capacity of 391.36 mg g⁻¹ for sulfonated lignite. The adsorption process of sulfonated lignite on biomorphic MgO was systematically investigated and was found to obey the pseudo-second-order rate equation and the Langmuir adsorption model. The negative values of Gibbs free energy change (ΔG) showed that the adsorption process was feasible and spontaneous. The endothermic process was depicted with a positive value for ΔH.

A biomorphic MgO nanomaterial was fabricated via a facile and low-cost immersion method using cotton as the template.     

Single-step synthesis of eucalyptus sawdust magnetic activated carbon and its adsorption behavior for methylene blue

Eucalyptus wood-based magnetic activated carbon (MAC) was prepared using single-step carbonization activation magnetization with FeCl₃ and utilized for the adsorption of methylene blue (MB). The MAC was prepared using the following conditions: the mass ratio of FeCl₃ to eucalyptus sawdust was controlled to 2 : 1, the one-step carbonated activated magnetization temperature and time was 700 °C and 75 min. The prepared MAC was evaluated for textural characteristics such as the adsorption capacity, pore structure, surface chemical functional groups, magnetic properties, microcrystalline structure, and the surface morphology using the test methods described in the National Standard of China, these were N₂-adsorption–desorption isotherms, Fourier transform infrared spectroscopy (FTIR), value stream mapping (VSM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Batch experiments were carried out to evaluate the adsorption behavior of MB on the prepared MAC at different temperatures of 298–328 K and MB initial concentration of 50.0–500.0 mg L⁻¹. The results were as follows: the iodine number, methylene blue adsorption and phenol adsorption of the prepared MAC were 473.14, 228.22 and 70.90 mg g⁻¹, respectively; MAC exhibited a microporous and mesoporous structure with a mesoporosity of 36%, the BET specific surface area, average pore diameter and pore volume were 645.23 m² g⁻¹, 2.71 nm and 0.44 cm³ g⁻¹, respectively, and for the magnetic parameters the following results were found, a H_c of 108.51 Oe, M_s of 30.37 emu g⁻¹ and M_r of 2.46 emu g⁻¹; there were OH, C–O, C O, C C, COO, C–N, and Fe–O groups on the MAC surface, and Fe₃O₄ existed in the pores and surfaces of the MAC. The MB adsorption on the MAC followed the Langmuir isotherm and Dubinin–Radushkevich isotherm model, the adsorption process was a spontaneous, endothermic chemisorption progress, followed by the pseudo-second-order model, and the adsorption process was influenced by multiple diffusion steps, the pore diffusion process was the rate-controlling step, however, the adsorption process was also affected by the film diffusion and surface adsorption. The results reveal that MAC efficiently adsorbs MB and can be easily separated and recovered by an external magnetic field. The as-prepared MAC could be used as a potential adsorbent for organic pollutant wastewater treatment.

Eucalyptus wood-based magnetic activated carbon (MAC) was prepared by single-step carbonization activation magnetization with FeCl₃ and utilized for the adsorption of methylene blue (MB).     

Broadening the pore size of coal-based activated carbon via a washing-free chem-physical activation method for high-capacity dye adsorption

Aiming to overcome the limitations of the narrow pore size distributions of traditional activated carbon materials and to achieve wide adaptabilities towards large molecules adsorption, we herein demonstrate a new type of activated carbon with a broadened pore size distribution for high-rate and high-capacity aqueous dye molecule (Rhodamine B) adsorption. The preparation of CP-AC is achieved by a facile and one-step mineral-assisted chem-physical activation strategy from Chinese large-reserve Zhundong coal with ZnCl₂ and CO₂ as the activation agents. The method yields the activated carbon (CP-AC) that has a pore-size broadened hierarchical pore configuration with a high surface area and a large pore volume, favorably enabling a high-capacity Rhodamine B adsorption up to 881 mg g⁻¹, which is among the highest levels of the reported activated carbons. A sonication-assisted adsorption test further demonstrates the high-rate adsorption capability of CP-AC with Rhodamine B adsorption capacity up to 842 mg g⁻¹ within 30 min (96% of the saturation capacity) while microporous activated carbon obtained by solely ZnCl₂ activation could just achieve a capacity of 374 mg g⁻¹ within 30 min. In virtue of the low-cost resource materials and washing-free craft, this work offers a simple and green preparation strategy towards high-performance coal based activated carbons, holding great potentials for the industrial production and applications.

Aiming to overcome the limitations of the narrow pore size distributions of traditional activated carbon, we demonstrate a new type of activated carbon with a broadened pore size distribution for high-rate and high-capacity aqueous dye adsorption.     

Recovery of NH4+–N and PO43−–P from urine using sludge-derived biochar as a fertilizer: performance and mechanism

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH₄⁺–N and PO₄³⁻–P from urine. The effects of dosage, adsorption time, and urine concentration on the adsorption of NH₄⁺–N and PO₄³⁻–P were investigated, and the adsorbed BS was used as a fertilizer to study its effect on the growth of pakchoi cabbage. The Elovich model was more consistent with the adsorption processes of NH₄⁺–N and PO₄³⁻–P. Both the NH₄⁺–N and PO₄³⁻–P adsorption isotherm model agreed with the Redlich–Peterson model. The Langmuir model showed that the largest adsorption capacity of BS600 for NH₄⁺–N and PO₄³⁻–P could reach 114.64 mg g⁻¹ and 31.05 mg g⁻¹, respectively. The NH₄⁺–N adsorption mechanism of BS may have complexation with O-containing functional groups and precipitation reactions, while the removal mechanism of PO₄³⁻–P was co-precipitation. The pot experiment demonstrated that adsorbed BS600 can better promote the growth of pakchoi cabbage with the same amount of addition. With the addition of 5% adsorbed BS600, the weight of cabbage was 64.49 g heavier than without the addition of BS600. This research provided theoretical support for the recovery of NH₄⁺–N and PO₄³⁻–P from urine as a fertilizer.

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH₄⁺–N and PO₄³⁻–P from urine.     

Bullet-like microstructured nickel ammonium phosphate/graphene foam composite as positive electrode for asymmetric supercapacitors

Unique microstructured nickel ammonium phosphate Ni(NH₄)₂(PO₃)₄·4H₂O and Ni(NH₄)₂(PO₃)₄·4H₂O/GF composite were successfully synthesized through the hydrothermal method with different graphene foam (GF) mass loading of 30, 60 and 90 mg as a positive electrode for asymmetric supercapacitors. The crystal structure, vibrational mode, texture and morphology of the samples were studied with X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy (SEM). The prepared materials were tested in both 3-and 2-electrode measurements using 6 M KOH electrolyte. The composite material Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg exhibited a remarkable gravimetric capacity of 52 mA h g⁻¹, higher than the 34 mA h g⁻¹ obtained for the Ni(NH₄)₂(PO₃)₄·4H₂O pristine sample, both at 0.5 A g⁻¹. For the fabrication of the asymmetric device, activated carbon from pepper seed (ppAC) was used as a negative electrode while Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg GF was adopted as the positive electrode. The Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg GF//ppAC asymmetric device delivered a specific energy of 52 Wh kg⁻¹ with an equivalent specific power of 861 W kg⁻¹ at 1.0 A g⁻¹ within a potential range of 0.0–1.5 V. Moreover, the asymmetric device displayed a capacity retention of about 76% for over 10 000 cycles at a high specific current of 10.0 A g⁻¹.

Unique morphology of (Ni(NH₄)₂(PO₃)₄·4H₂O/60GF) as a positive electrode for high-performance asymmetric supercapacitors.     

Removal of aqueous Hg(ii) by thiol-functionalized nonporous silica microspheres prepared by one-step sol–gel method

It is well known that thiol-functionalized silica (SiO₂-SH) can be used as an effective adsorbent for the removal of Hg(ii) from water. Studies in this field have focused on porous silica gels and mesoporous silicas that have large surface area and pore volume, while nonporous silica particles are seldom reported. This work aims to investigate the Hg(ii) adsorption properties of nonporous SiO₂-SH microspheres prepared by a simple one-step sol–gel method. The effects of pH, initial concentration of Hg(ii) and temperature on the adsorption properties of the SiO₂-SH microspheres were studied via batch adsorption experiments. The maximum adsorption capacity for Hg(ii) at 293 K calculated from the Langmuir equation was 377.36 mg g⁻¹. The adsorption kinetics and equilibrium data were well-fitted to the pseudo-second-order model and the Langmuir isotherm model, respectively.

The adsorption properties of nonporous SiO₂-SH microspheres prepared by a one-step sol–gel method for Hg(ii) in water were studied.     

Ultrasonic-assisted preparation of highly active Co3O4/MCM-41 adsorbent and its desulfurization performance for low H2S concentration gas

Co₃O₄/MCM-41 adsorbents were successfully prepared by ultrasonic assisted impregnation (UAI) and traditional mechanical stirring impregnation (TMI) technologies and characterized by X-ray diffraction (XRD), N₂ adsorption desorption, Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry-differential thermal analysis (TG-DTA). The H₂S removal performances for a simulated low H₂S concentration gas were investigated in a fixed-bed. The effect of preparation and adsorption conditions on the H₂S removal over Co₃O₄/MCM-41 were systematically examined. The results showed that UAI promotes more and well defined highly dispersed active Co₃O₄ phase on MCM-41. As compared to the Co₃O₄/MCM-41-T prepared via TMI, the saturated H₂S capacity of Co₃O₄/MCM-41-U prepared via UAI improved by 33.2%. The desulfurization performance of adsorbents decreased in the order of Co₃O₄/MCM-41-U > Co₃O₄/MCM-41-T > MCM-41. The Co₃O₄/MCM-41-U prepared using Co(NO₃)₂ concentration of 10%, ultrasonic time of 2 h, calcination temperature of 550 °C and calcination time of 3 h exhibited the best H₂S removal efficiency. At adsorption temperature of 25 °C with model gas flowrate of 20 mL min⁻¹, the breakthrough time of Co₃O₄/MCM-41-U was 10 min, and the saturated H₂S capacity and H₂S removal rate was 52.6 mg g⁻¹ and 47.8%, respectively.

Co₃O₄/MCM-41 adsorbent with high surface area and more active sites was successfully prepared by ultrasonic assisted impregnation (UAI) technology and it has been found that the sulfur capacity was improved by 33.2% because of ultrasonication.     

Sodium dodecylsulfate-layered double hydroxide and its use in the adsorption of 17β-estradiol in wastewater

Modified Mg₃Al layered double hydroxide (LDH) intercalated with dodecylsulfate anion composites, which were designated as SDS-LDH composites, were synthesized by coprecipitation. The samples were characterized using SEM, EDX, FT-IR, zeta potential analysis, and XRD. The results showed that the SDS-LDH composites contain a thicker and larger porous interconnected network than inorganic LDH due to the enlarged inter-layer distance. The outstanding adsorption performance of SDS-LDH composites toward 17β-estradiol (E2) was investigated under different conditions, including solution pH, adsorbent dosage, ion strength, reaction time, and temperature. When the solution pH was 7 and the adsorbent dosage was 2 g L⁻¹, the removal rate of E2 reached the maximum at 94%, whereas inorganic LDH displayed a poor E2 removal rate of 10%. The presence of various ions (Na⁺, SO₄²⁻, CI⁻, and H₂PO₄⁻) in aqueous solution exerted no significant adverse effects on the adsorption process. The adsorption equilibrium was reached within 20 min, and the adsorption fitted well with the pseudo-second-order model and the Freundlich isotherm. The thermodynamic test revealed that the adsorption process was spontaneous and endothermic. Phosphorus was selected as the index for evaluating the adsorption capacity of SDS-LDH composites for inorganic ions. The removal rates of total phosphorus and PO₄³⁻ were 43.71% and 55.93% for SDS-LDH composites at 2 g L⁻¹. The removal rate of PO₄³⁻ reached up to 85% when the contact time was 120 min and the dosage was 3 g L⁻¹ for SDS-LDH composites, which were approximately close to those of inorganic LDH of 30 min and 2 g L⁻¹, respectively. This finding indicates that the removal capacity of SDS-LDH composites for PO₄³⁻ decreased after the dodecylsulfate anions intercalated into the interlayer. The composites retained their high efficiency and stability after desorption and regeneration with alkali treatment. This study demonstrated that SDS-LDH composites are a promising adsorbent for the recovery and abatement of trace-level E2 in secondary effluents of wastewater treatment plants.

SDS-LDH composites were synthesized by coprecipitation. The composites are promising adsorbents for the recovery and abatement of trace-level E2 in secondary effluents of wastewater treatment plants.     

Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F− and Cl− in phosphorus-rich solutions

The magnetic nano-adsorbent Fe₃O₄@Mg/Al-CO₃-LDH (Mg/Al-type layered double hydroxide) with a CO₃²⁻ interlayer anion has been synthesized successfully on Fe₃O₄ nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO₄³⁻ rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F⁻ and Cl⁻, even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO₄³⁻ in phosphorus-rich solutions, and especially can be utilized to determine trace F⁻ and Cl⁻ anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO₄³⁻ for trace determinations. Herein, the hydrothermally synthesized Fe₃O₄@Mg/Al-CO₃-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe₃O₄@Mg/Al-CO₃-LDH was utilized successfully to adsorb PO₄³⁻ in real samples and determine trace F⁻ and Cl⁻ accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO₄³⁻ in phosphorus-rich samples, leaving F⁻ and Cl⁻ even if in a trace content.

Synthesized recyclable Fe₃O₄@Mg/Al-CO₃-LDH magnetic nano-adsorbent is utilized to dephosphorize phosphorous-rich solutions but leave F⁻ and Cl⁻ to be detected chromatographically.     

Effect of lignite as support precursor on deep desulfurization performance of semicoke supported zinc oxide sorbent in hot coal gas

In this study, four different semicoke supported zinc oxide sorbents were prepared by combining high-pressure impregnation and heat treatment using four different lignites (Zhaotong, Xiaolongtan, Huolinhe, and Shengli districts) as precursors of supports and zinc nitrate as precursor of the active component. Their desulfurization performances were studied in a fixed-bed reactor at 400 °C in simulated coal gas. The physico-chemical properties of raw lignites were investigated using chemical titration, nitrogen adsorption and thermogravimetry (TG). The physico-chemical structures of sorbents were characterized by atomic absorption spectrometry (AAS), X-ray diffraction analysis (XRD), nitrogen adsorption, and scanning electron microscopy (SEM). The results indicate that the lignite as support precursor plays a critical role in the desulfurization performance of the sorbent. It affects the desulfurization activity of the prepared sorbent by influencing the loading content and utilization rate of the active component of the sorbent. The sorbent HPZn/C(Z) prepared using Zhaotong lignite presents the best desulfurization performance owing to its higher content and utilization rate of the active component, with a 13.74 h breakthrough time with the breakthrough sulfur capacity of 3.69 g sulfur/100 g sorbent. It is found that the loading content of the active component depends on the pore structure of the raw lignite, how its pore structure changes in high-pressure impregnation process and the content of oxygen-containing functional groups on its surface. The utilization rate of the active component is associated with the pore structure properties of the sorbent formed during heat treatment.

Effect of lignite as support precursor on desulfurization performance of semicoke supported zinc oxide sorbent.     

Performance of a zeolite modified with N,N-dimethyl dehydroabietylamine oxide (DAAO) for adsorption of humic acid assessed in batch and fixed bed columns

Factors that affect adsorption of a synthetic humic acid (HA) on a zeolite modified with the surfactant N,N-dimethyl dehydroabietylamine oxide (DAAO) (SMZ) were investigated in batch and fixed bed column experiments. Adsorption increased with increasing HA concentrations and contact time, but decreased with increasing pH, temperature, and ionic strength. Adsorption of HA on SMZ was increased by the presence of the cations Ca²⁺ and Mg²⁺, whereas anions such as NO₃⁻, HCO₃⁻, SO₄²⁻, and PO₄³⁻ showed the opposite trend, and competed with HA adsorption. HA adsorption on SMZ was well-fitted by pseudo-second order kinetics, and described by the Langmuir isotherm model. The maximum adsorption capacity in batch experiments calculated from the Langmuir adsorption isotherm was about 126 mg g⁻¹. Thermodynamic calculations showed that HA adsorption on the zeolite with bilayer DAAO coverage was spontaneous and exothermic. Optimum desorption was obtained using 0.1 M NaOH with a recovery of 94%. The HA adsorption capacity of SMZ at the breakthrough point was greatly influenced by bed depth, and could be described by the Thomas model. Adsorption mechanisms are interpreted as involving mainly hydrogen bonding and electrostatic interactions.

Factors that affect adsorption of a synthetic humic acid (HA) on a zeolite modified with the surfactant N,N-dimethyl dehydroabietylamine oxide (DAAO) (SMZ) were investigated in batch and fixed bed column experiments.     

One-step preparation of a novel SrCO3/g-C3N4 nano-composite and its application in selective adsorption of crystal violet

A novel kind of nanoparticle SrCO₃/g-C₃N₄ was prepared using strontium carbonate (SrCO₃) and melamine (C₃H₆N₆) as raw materials via one-step calcination. The formation of SrCO₃/g-C₃N₄ was confirmed from the X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) analysis. Its selective adsorption performance was evaluated towards crystal violet (CV), rhodamine B (RhB) and methylene blue (MB). The results showed that the SrCO₃/g-C₃N₄ had selective adsorption ability of CV. Furthermore, adsorption measurements of CV were conducted to investigate the influences of contact time, initial concentration, initial dye solution pH value and adsorbent dosage. The maximum removal rate of CV was 98.56% when the initial concentration was 1600 mg L⁻¹. The kinetic study indicated the adsorption of CV followed the pseudo-second-second model well. The adsorption efficiency of SrCO₃/g-C₃N₄ was greater (97.46%) than that of g-C₃N₄ (31.30%) and SrCO₃ (17.30%). It could be deduced that the synergistic effect of conjugation interaction of g-C₃N₄ and the electrostatic attraction of SrCO₃ might be the main driving force for the superb adsorption of CV.

A novel kind of nanoparticle SrCO₃/g-C₃N₄ was prepared using strontium carbonate (SrCO₃) and melamine as raw materials via one-step calcination.     

Effect of mass ratio on micro-mesoporous Cu-SSZ-13/CeWTi composite catalysts for the selective catalytic reduction of NO with ammonia

A series of micro-mesoporous SSZ-13/CexWyTiz composites with different zeolite/oxide ratios were synthesized using a one-step crystallization method. The effects of the mass ratio on the crystal form, specific surface area, pore structure, surface element properties, redox properties, surface acidity and deNO_x performance of the Cu-SSZ-13/CeWTi composite catalysts were investigated using X-ray diffractometry (XRD), Brunauer–Emmett–Teller analysis (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature programmed reduction (H₂-TPR) and NH₃ temperature programmed desorption (NH₃-TPD). The results reveal that the Cu-SSZ-13/CeWTi composite catalysts formed a micro-mesoporous structure. The increase in the mass ratio leads to the increased microporous ratio of the composite catalysts, the improved crystal structure of SSZ-13 and a higher specific surface area and pore volume, which is conducive to enhancing the low-temperature deNO_x activity, but its high-temperature performance (450 °C and above) decreases. The introduction of micropores into mesoporous materials can result in the production of more Ce⁴⁺, surface chemisorption oxygen species O_α and acid sites. The Cu-SSZ-13/CeWTi composite catalyst with a mass ratio of 1 : 4 demonstrated the best micro-mesoporous ratio, low-temperature selective catalytic reduction (SCR) performance and hydrothermal stability.

A series of micro-mesoporous SSZ-13/CexWyTiz composites with different zeolite/oxide ratios were synthesized using a one-step crystallization method.     

Effect of H2SO4/H2O2 pre-treatment on electrochemical properties of exfoliated graphite prepared by an electro-exfoliation method

The effect of pre-treating graphite sheets in a H₂SO₄/H₂O₂ solution before electro-exfoliation is reported. It was revealed that the volume fraction of H₂SO₄ to H₂O₂ during pre-treatment could control the degree of exfoliation of the resulting exfoliated graphite (EG). X-ray diffraction (XRD), Raman, and Fourier transform infrared (FTIR) spectroscopy analyses have suggested that EG produced by first pre-treating the graphite sheet in H₂SO₄/H₂O₂ solution with the H₂SO₄ : H₂O₂ volume fraction of 95 : 5 demonstrates the highest exfoliation degree. This sample also demonstrated excellent electrochemical properties with good electrical conductivity (36.22 S cm⁻¹) and relatively low charge transfer resistance (R_ct) of 21.35 Ω. This sample also showed the highest specific capacitance of all samples, i.e., 71.95 F g⁻¹ at 1 mV s⁻¹ when measured at a voltage range of −0.9 to 0 V. Further measurement at an extended potential window down to −1.4 V revealed the superior specific capacitance value of 150.69 F g⁻¹. The superior morphology characteristics and the excellent electrical properties of the obtained EG are several reasons behind its exceptional properties. The pre-treatment of graphite sheets in H₂SO₄/H₂O₂ solution allegedly leads to easier and faster exfoliation. The faster exfoliation is allegedly able to prevent massive oxidation, which frequently induces the formation of graphite/graphene oxide (GO) in a prolonged process. However, too large H₂O₂ volume fraction involved during pre-treatment seems to cause excessive expansion and frail structure of the graphite sheets, which leads to an early breakdown of the structure during electrochemical exfoliation and prohibits layer by layer exfoliation.

Early expansion of graphite after H₂SO₄/H₂O₂ pre-treatment and cyclic voltammograms of exfoliated graphite (EG) prepared with various volume fractions of H₂O₂.     

Study of the Fischer–Tropsch synthesis on nano-precipitated iron-based catalysts with different particle sizes

Nano iron-based catalysts with different particle sizes were prepared by a co-precipitated method and characterized by XRD, N₂ adsorption, SEM, Mössbauer spectroscopy, XPS, H₂-TPR, CO-TPD, H₂-TPD and TGA. The CO-TPD results revealed that large particle sizes of catalysts were not conducive to the adsorption of CO, and exhibited low activity of FTS. The decrease of catalyst particle size enhanced the interaction between Fe and Mn, and promoted the CO chemical adsorption and the formation of Fe₅C₂, but the hydrogenation reaction was inhibited as confirmed by H₂-TPD. When the particle size continued to decrease, Mössbauer spectroscopy showed that MnFe₂O₄ appeared in the catalyst phase, which hindered the reduction of catalysts and the adsorption of feed gas. Overall, the sample FeMnSm-600 showed the highest C _2–4 selectivity of 33% at the highest CO conversion of 79% during the reaction conditions of 300 °C, 1.0 MPa, 12 000 mL (g h)⁻¹, and H₂/CO = 2.

Fischer–Tropsch synthesis of nano iron-based catalysts with different particle sizes were prepared by a precipitated method.     

A novel one-step synthesis of Ce/Mn/Fe mixed metal oxide nanocomposites for oxidative removal of hydrogen sulfide at room temperature

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions. The microscopic images confirmed polyhedral nanocrystals of 10–20 nm size, clustered to form nanospheres. The elemental mapping confirmed the uniform distribution of transition metal oxides in the CeO₂ matrix. The X-ray diffraction analysis confirmed the phase purity of metal oxides in nanocomposites. The surface area of nanocomposites was in the range of 16–21 m² g⁻¹. X-ray photoelectron spectroscopy confirmed 25–28% of Ce³⁺ ions in the CeO₂ of nanocomposites. These nanocomposites were tested for the removal of hydrogen sulfide gas at room temperature. The maximum adsorption capacity of 28.3 mg g⁻¹ was recorded for CeO₂/Mn₂O₃/Fe₂O₃ with 500 ppm of H₂S gas and 0.2 L min⁻¹ of flow rate. The adsorption mechanism probed by X-ray photoelectron spectroscopy showed the presence of sulfate as the only species formed from the oxidation of H₂S, which was further confirmed by ion chromatography. Thus, the study reports room-temperature oxidation of H₂S over mixed metal composites, which were synthesized by a novel one-step approach.

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions.     

Simultaneous immobilization of NH4+ and Mn2+ from electrolytic manganese residue using phosphate and magnesium sources

Immobilization of contaminants from electrolytic manganese residue (EMR) is essential for the safe stacking and reuse of EMR. This study provides experiment results for the simultaneous immobilization of NH₄⁺ and Mn²⁺ from EMR using Na₃PO₄·12H₂O and MgSO₄·7H₂O (PS) agents, as well as Na₃PO₄·12H₂O and MgO (PO) agents. The optimum reaction conditions, characteristics of immobilization, mechanism and the economy of alternative chemicals were determined and are discussed. The results indicated that the immobilization efficiencies of NH₄⁺ and Mn²⁺ were 92.4% and 99.9% respectively under the following conditions: a MgSO₄·7H₂O : Na₃PO₄·12H₂O : EMR mass ratio of 0.113 : 0.175 : 1, a CaO : EMR mass ratio of 0.03 : 1 and a reaction time of 1 h using PS agents. The concentration of NH₄⁺ in the leach liquor reduced from 1264 to 98 mg L⁻¹ after immobilization. The concentration of heavy metal ions decreased sharply in the leach liquor and met the Integrated Wastewater Discharge Standard of China (GB8978-1996). The characteristics of immobilization indicated that NH₄⁺ was immobilized to form NH₄MgPO₄·6H₂O and that Mn²⁺ was immobilized to form Mn₅(PO₄)₂(OH)₄, Mn₃(PO₄)₂·3H₂O and Mn(OH)₂. An economic evaluation showed that using PS agents had lower associated cost than using PO agents.

Immobilization of contaminants from electrolytic manganese residue (EMR) is essential for the safe stacking and reuse of EMR.