Site Energy Distribution Research Articles

Hollow microspheres of layered double hydroxides through surfactant-free method enhanced heavy metals removal from soil

A three-dimensional MgAl layered double hydroxides hollow microsphere (HMS-LDH) is fabricated by surfactant-free method. The microstructure and the formation mechanism of HMS-LDH are investigated by XRD (X-ray diffraction), SEM (Scanning Electron Microscope), EDS (Energy dispersive Spectrometer) and XPS (X-ray photoelectron spectrometer). The morphology of LDHs could be varied by changing the ratio of metal cations to urea. The adsorption properties of HMS-LDH for heavy metals from soil are investigated. The results of experiments demonstrates that the adsorption kinetics of Cu(Ⅱ), Pb(Ⅱ), As(Ⅴ), Cr(Ⅵ) are in good agreement with the pseudo-second-order kinetic and intraparticle diffusion model. The adsorption isotherm data of Cu(Ⅱ)/Pb(Ⅱ) is accordance with the Langmuir-Freundlich model, while the equilibrium adsorption of As(Ⅴ)/Cr(Ⅵ) follow the Generalized-Langmuir isotherm model well. Site energy distribution theory denotes the hollow microsphere structure increases the adsorption sites of heavy metals, which is conducive to the adsorption process. The different mechanisms of precipitation for Cu(Ⅱ)/Pb(Ⅱ) removal and interlayer adsorption for As(Ⅴ)/Cr(Ⅵ) removal are proposed. The effects of coexisting cations and column leaching experiments on the performance evaluation are also investigated, which indicate most the ions have no effect on the adsorption of Cu (Ⅱ)/Pb(Ⅱ) and As(Ⅴ)/Cr(Ⅵ). This work proposes a simple approach to prepare LDHs hollow microspheres and demonstrates their excellent properties for the remediation of heavy metal polluted soil.

Nanoporous carbons from hydrothermally pre-treated avocado waste: experimental design, hydrogen storage behavior, and energy distribution analysis

AbstractAvocado waste, which includes the peel and seed, is a promising biomass source for highly porous materials crucial to establishing an economical and efficient hydrogen economy. Hydrothermally pre-treated avocado waste was explored as a precursor for biocarbon optimized for hydrogen storage, employing the design of experiment to vary activation temperature and impregnation ratio. The resulting optimized biocarbon, synthesized at 800 °C with a 1:3 impregnation ratio, exhibited appreciable hydrogen uptake at 77 K and 1 bar, surpassing some reported literature values. Notably, the optimized biocarbon (AC200), hydrothermally pretreated at 200 °C, demonstrated a remarkable 3.07 wt% hydrogen uptake, attributed to its narrower micropores facilitating extensive adsorption. The study employed a modified Langmuir model incorporating homotattic patch approximation for a universal isotherm model, providing insights into the surface characteristics of the optimized biocarbon in terms of adsorption site availability and energy distribution. The modeling offers insight into the heterogeneous surface characteristics, specifically regarding the availability of adsorption sites, elucidating the distinct behavior exhibited by each optimized biocarbon.

Efficient removal of nitrophenol by magnetic ion exchange resins: Role of nitrophenol functional groups based on characterisation, DFT calculations and site energy distributions

The diverse locations of functional groups on different nitrophenol cause uncertainty concerning the removal efficiency and mechanisms of nitrophenol. Adsorption behavior and mechanisms of nitrophenol pollutants (2-nitrophenol (ONP) and 4-nitrophenol (PNP)) on magnetic ion exchange (MIEX) resin were investigated by a combination method of characterization, DFT calculations, and site energy analysis. The results showed pore filling, hydrophobicity, hydrogen bonding, van der Waals forces, π-π conjugation, ion exchange, and electrostatic attraction were included in the removal mechanisms. Solution pH influenced the adsorption mechanism by inducing electrostatic attraction, hydrogen bonding and ion exchange. DFT calculations found that hydrogen bonding was the dominant action among the removal mechanisms for the nitrophenol existing in the form of a molecular state. But distinguished from the removal of PNP by the interaction of hydrogen bonds (O⋯H-N) between the –NO2 in PNP and the –NH-CO– group in MIEX resin, the ONP was mainly removed by hydrogen bonds (H⋯O-C) between the –OH functional group in ONP and the –COOH functional group in MIEX resin. However, the ionic nitrophenol pollutants were mainly removed through electrostatic attraction and ion exchange. Increasing resin dosage facilitated the removal of nitrophenol. Humic acid demonstrated little effect. Sulfate ions showed the most severe inhibition on the removal of nitrophenol. Equilibrium was achieved after 60 min. The adsorption process was well described using the Sips isotherm. The main rate-limiting step was liquid film diffusion. Site energy analysis found that the affinity of PNP for MIEX resin was higher, and the removal of PNP was more susceptible to temperature compared to ONP. A 1.0 % sodium chloride could effectively regenerate the saturated resin, and the adsorption efficacy did not decrease significantly after four adsorption–desorption cycles. Therefore, MIEX resin has a good potential for the control of nitrophenol in polluted water sources.

Polyamide 6 microplastics as carriers led to changes in the fate of bisphenol A and dibutyl phthalate in drinking water distribution systems: The role of adsorption and interfacial partitioning

Microplastics (MPs) co-exist with plastic additives and other emerging pollutants in the drinking water distribution systems (DWDSs). Due to their strong adsorption capacity, MPs may influence the occurrence of additives in DWDSs. The article investigated the occurrence of typical additives bisphenol A (BPA) and dibutyl phthalate (DBP) in DWDSs under the influence of polyamide 6 (PA6) MPs and further discussed the partitioning of BPA/DBP on PA6s, filling a research gap regarding the impact of adsorption between contaminants on their occurrence within DWDSs. In this study, adsorption experiments of BPA/DBP with PA6s and pipe scales were conducted and their interaction mechanisms were investigated. Competitive adsorption experiments of BPA/DBP were also carried out with site energy distribution theory (SEDT) calculations. The results demonstrated that PA6s might contribute to the accumulation of BPA/DBP on pipe scales. The adsorption efficiencies of BPA/DBP with both PA6s and pipe scales were 26.47 and 2.61 times higher than those with only pipe scales. It was noteworthy that BPA had a synergistic effect on the adsorption of DBP on PA6s, resulting in a 26.47 % increase in DBP adsorption. The article provides valuable insights for the compounding effect of different types of additives in water quality monitoring and evaluation.

Theoretical approach of hydrogen absorption isotherms on C14–Zr(Cr0.5Ni0.5)2 Laves phases

Theoretical studies on the total energy, and hydrogen absorption thermodynamics on Zr(Cr0.5Ni0.5)2 intermetallic compound were performed using absorption models on the most stable sites. In the first stage, Density Functional calculations provide the absorption energies corresponding to hydrogen in different environments. From there, 28 hydrogen absorption locations were found and the corresponding absorption energies were specifically determined. Then, with this information, a theoretical approximation based on the concept of local absorption isotherm and Fermi-Dirac statistics was applied to study the thermodynamics of the system. In this case, and due to the absence of lateral interactions, exact expressions of the thermodynamic functions can be derived. The process was monitored by following the surface coverage as a function of the chemical potential (absorption isotherm), the energy and configurational entropy of the adsorbed phase and the differential heat of absorption. Interesting behaviours were observed and discussed in terms of the absorption microscopic properties (energy distribution of the absorption sites).

Enhanced adsorption of phosphate by rice straw-based biochar prepared via metal impregnation and bio-template technology.

Phosphate removal from water through green, highly efficient technologies has received much attention. Biochar is an effective adsorbent for phosphate removal. However, adsorption capacity of phosphate on pristine rice straw-based biochar was not optimistic due to low anion exchange capacity. In this study, Fe-modified, Mg-modified and MgFe-modified rice straw-based biochar (Fe-BC, Mg-BC and MgFe-BC) were prepared by combining metal impregnation and biological template methods to improve the adsorption capacity of phosphate. The surface characteristics of biochar and the adsorption behavior of phosphate on biochar were investigated. The modified biochar had the specific surface area of 17.910-39.336 m2/g, and their surfaces were rich in a large number of functional groups and metal oxides. Phosphate release was observed on pristine rice straw-based biochar without metal impregnation. The maximum adsorption capacities of phosphate on MgFe-BC, Mg-BC and Fe-BC at 298K were 6.93, 5.75 and 0.23mg/g, respectively. Adsorption was a spontaneous endothermic process, while chemical adsorption dominated and electrostatic attraction and pores filling existed simultaneously. Based on the site energy distribution theory study, the standard deviation of MgFe-BC decreased from 6.96 to 4.64kJ/mol with temperature increasing, which proved that the higher the temperature would cause the lower heterogeneity. Moreover, the effects of pH, humic acid, co-existing ions and ionic strength on phosphate adsorption of MgFe-BC were also discussed. MgFe-BC with fine pores and efficient adsorption sites is an ideal adsorbent for phosphate removal from water.

Statistical physics investigation of the docking process of fruity odorants on Machilis hrabei MhOR5: New microscopic interpretations

In this paper, the putative phenomenon of adsorption involved in the insect olfactory perception of four fruity odorants on Machilishrabei olfactory receptor MhOR5 was studied at a molecular scale. Thus, the experimental concentration–response curves of propyl acetate, butyl acetate, isobutyl acetate, and prenyl acetate on MhOR5 were adjusted using the monolayer model of ideal gas established using the powerful statistical physics approach, which was selected as the most appropriate model among the others. The fitted model parameters were applied to stereographic and energetic analyze the four olfactory systems. Indeed, the modeling results indicated that the tested fruity key food odorants (KFOs) were docked as 2- or 3-aggregated molecules on one MhOR5 binding site via a nonparallel position (i.e., multi-molecular adsorption mechanism). Energetic parameters were used to characterize the adsorption process involved in the studied systems via the determination of the molar adsorption energies (ranging from 12.91 to 17.52 kJ/mol). Hence, the values of the molar adsorption energies are positive and inferior to 40 kJ/mol; this means that the putative adsorption mechanism presented an exothermic character and a physical type. The docking simulation results proved that the adsorption of propyl acetate, butyl acetate, isobutyl acetate, and prenyl acetate on MhOR5 may occur via physical interactions (weak interactions) like alkyl, pi-alkyl, van der Waals, carbon hydrogen bond, and conventional hydrogen bond. The statistical physics theory may also be utilized to quantitatively characterize Machilishrabei MhOR5 activated by propyl acetate, butyl acetate, isobutyl acetate, and prenyl acetate odorants via the estimation of the different site size distributions (SSDs) and site energy distributions (SEDs).

Comparative analysis of CO2 and N2 adsorption on zeolite 4A: Thermodynamics parameters and site energy distribution investigations

Adsorption equilibrium data for CO2 and N2 on zeolite 4A were volumetrically measured at temperatures ranging from 278 K to 328 K and gas pressures up to 4 MPa. The experimental data was correlated using the high-pressure Langmuir, Sips, and DA adsorption isotherm models. The high-pressure DA model was found to be the optimal model for describing the adsorption isotherms on basis of nonlinear regression analysis. Subsequently, the thermodynamic parameters, including isosteric heat of adsorption (Hst), adsorption phase specific heat capacity (cpa), adsorption phase entropy (sa), and enthalpy (ha), considering the actual adsorption state, were estimated. The results demonstrate that the adsorption of CO2 on zeolite 4A is greater than that of N2. The higher Hst and ha values and the lower sa values of CO2 compared to N2, suggest a stronger surface interaction of CO2 with zeolite 4A, resulting in a more ordered arrangement of CO2 molecules than N2. Site energy distribution theory analysis indicates that less energy is required for CO2 adsorption and greater site energy heterogeneity of CO2 than those of N2 on zeolite 4A. The obtained results evidence that the studied zeolite 4A could be a promising candidate adsorbent for greenhouse gas capture.

Adsorption of anionic dyes from aqueous solutions by a novel CTAB/MXene/carbon nanotube composite: Characterization, experiments, and theoretical analysis

A novel three-dimensional composite was prepared by the self-assembly of MXene nanosheets and carbon nanotubes (CNTs) with the assistance of cetyltrimethylammonium bromide (CTAB), which was named as CMC composite. Adsorption of three anionic dyes, including Acid orange (AO7), Methyl orange (MO) and Congo red (CR), from aqueous solutions on the composite and the mechanisms were investigated in this study. Compared with MXene and CNTs, the CMC composite exhibited superior adsorption performance for AO7, MO and CR with maximum adsorption capacities of 367.9, 294.2, and 628.5 mg/g, respectively. The adsorption capacities of AO7 and MO on the CMC composite decreased, while that of CR increased with increasing temperatures. Quantum chemical calculations indicated that electrostatic interactions, π-π electron-donor-acceptor interactions and hydrogen bonding played important roles on the adsorption. The approximate site energy distribution analysis demonstrated that more adsorption active sites existed on the CMC composite than on MXene and CNTs, which endowed the CMC composite with higher adsorption capacities for these anionic dyes. The differences of adsorption behaviors for three anionic dyes could be ascribed to the number of available adsorption sites and the change of the site heterogeneity on the CMC surface.

Adsorption of atrazine and paraquat on montmorillonite loaded with layered double hydroxide and active site energy distribution analysis

Abstract Clay minerals are effective adsorbents for the remediation of pesticides in wastewater due to their large superficial areas and excellent cation-exchange capabilities. However, this adsorption effect can be reduced by the accumulation of adsorbents on clay minerals, amongst other problems. Therefore, in this study, montmorillonite (Mnt) modified by layered double hydroxide (LDH) with different loading amounts was successfully prepared using an in situ method. The results from X-ray diffraction, Fourier-transform infrared spectrometry, Brunauer–Emmet–Teller (BET) and scanning electron microscopy analyses revealed that LDH structures were successfully combined with the Mnt layer and formed a porous structure. However, excess LDH still caused the aggregation and accumulation of layers. The adsorption performance of LDH@Mnt for atrazine (ATZ) and paraquat (PQ) was investigated, and the removal efficiency of the LDH@Mnt composite was higher than those of Mnt and LDH alone. The kinetic study revealed that the adsorption process fitted the pseudo-second-order model and internal diffusion model, and 3-LDH@Mnt had the greatest absorbability efficiency for both ATZ and PQ, indicating the adsorption process was controlled by the number of active sites of the adsorbent. The generalized Langmuir model accurately characterized the adsorption process of ATZ and PQ elimination in the adsorption isotherm investigation, indicating that the adsorption energies of the active sites on the adsorbents were different. 3-LDH@Mnt had better absorbability performance for ATZ/PQ, and the sorption capacities were 7.03 and 91.9 mg g–1, respectively. According to site energy distribution theory, the amount of sorption sites of the composite adsorbent was large and the average adsorption energy was high, both of which being beneficial for the adsorption of ATZ and PQ. The effects of pH, coexisting anions and reuse experiments were also tested, indicating that the LDH@Mnt composite possessed high adsorption stability. This excellent removal performance represents a promising strategy for the remediation and elimination of pesticide contaminations from the environment.

Effect of iron nanoparticles on chromium adsorption in aqueous solution using magnetic biochar: A site energy distribution analysis

The effects of adding green-synthesized magnetic iron-containing nanoparticles (GSMFe) onto biochar in aqueous solution for the adsorptive removal of hexavalent chromium [Cr(VI)] were investigated in this study. Nanocomposites, denoted as green synthesis magnetic biochar (GSMB), were created using a green synthesis technique with white tea residue to introduce GSMFe into biochar. Six adsorbents, varying in GSMFe content, were tested for their effectiveness in eliminating Cr(VI), a globally significant hazardous heavy metal. The results demonstrated that incorporating GSMFe into biochar led to significant improvements in adsorption capacity and saturation magnetization. With an increasing amount of GSMFe, the maximum adsorption capacity increased from 2.47 mg/g (EWTWB) to 9.11 mg/g (GSMB4). The highest saturation magnetization was achieved at 13.4 Am2/kg at GSMB4. Similarly, surface areas rose up to 72.9 m2/g at GSMB3 but declined thereafter due to GSMFe aggregation and pore blockage. Sorption behavior for Cr(VI) was assessed using five isotherm models, with the Redlich-Peterson model showing the best fit. The analysis of approximate site energy distribution (SED) indicates that the incorporation of GSMFe enhances the frequency of the entire range of sorption energy sites, while the biochar matrix contributes to a slight increase in medium sorption energy sites within the GSMFe. Among the GSMBs, the difference were more pronounced at low-energy sites than at high-energy sites. At higher energy sites (27,500–40,000 J/mol), sorption site frequencies remained similar, regardless of GSMFe content and associated physicochemical properties. For sorption energy site values exceeding 17,500 J/mol (Cr(VI) concentration below 50 mg/L), GSMB2 is regarded as a more practical choice due to its relatively large area under the frequency distribution curve and commendable cost-effectiveness.

Removal of pesticides by layered double hydroxide modified different clay minerals and site energy analysis

Layered double hydroxides (LDHs) modified montmorillonite, mica, illite, and chlorite to from composites adsorbents of LDH@Mt, LDH@Mi, LDH@Ill, and LDH@Chl were prepared for removal of atrazine (ATZ) and 4-chloro-2-methylphenoxyacetic acid (MCP), and characterized through XRD, FT-IR, BET, and SEM analyses. In kinetics study, four composite adsorbents well fitted pseudo-second-order kinetics and intraparticle diffusion. Generalized Langmuir model described adsorption process better than Langmuir model in isothermal study, indicating there were heterogeneous adsorption sites for ATZ/MCP on adsorbents. LDH@Mt possessed better adsorption performance for ATZ/MCP, and the adsorption capacities are 8.19 mg/g and 90.9 mg/g, respectively. Theory of site energy distribution analyzed the number of adsorption sites qualitatively, and showed that the accessible adsorption sites on LDH@Mt were more than that of other adsorbents. Thermodynamic analysis revealed that the removal processes were endothermic and spontaneous. The removal of ATZ/MCP by LDHs modified clays offers an effective approach for pesticides removal.

Manifestation of site energy landscapes for ion transport in borate glasses.

The potential energy landscape of lithium borate glass of composition Li3B7O12 has been investigated by the charge attachment induced transport (CAIT) technique. Here, native lithium ions have been replaced by foreign alkali ions, M+ = K+, Rb+, Cs+. All experiments exhibit a pronounced decrease of native ion diffusion coefficients over more than 4 orders of magnitude with decreasing local population of Li+. The energy landscape is modelled by a site energy distribution (SED) with a concentration dependent Fermi energy of the native Li+ ions. The width of the populated part of the SED is found to be 250 meV (FWHM). The conclusion is made possible by a combination of a macroscopic ion replacement experiment with a Nernst-Planck-Poisson modelling of concentration depth profiles measured by secondary ion mass spectrometry (SIMS). Possible generalizations of macroscopic transport theory to match an Onsager ansatz are discussed.

Cr(VI) adsorption on activated carbon, sludge derived biochar, and peanut shells derived biochar: Performance, mechanisms during the reuse process and site energy distribution analysis

The reusability of adsorbents for Cr(VI) removal and the related mechanism are important to practical application. In this study, commercial activated carbon (AC), sludge-derived biochar (SBC), and peanut shell-derived biochar (PBC) were reused to the tenth round on Cr(VI) removal and then characterized to analyze the ongoing adsorption mechanisms involved during the reuse process. The site energy distribution theory was used to analyze the changes in site energy during the reuse of synthesized adsorbents. Batch adsorption experiments revealed that Cr(VI) removal efficiency decreased from 99.97 % to 43.37 %, 47.22 %, and 40.13 % when reusing AC, SBC, and PBC, respectively, from the first to the tenth round at optimum conditions. The adsorption capacity decreased with each reuse round due to a decrease in -OH, CO, O=C-O, and CO on the surface of adsorbents. The site energy (E*) values decreased as adsorption capacity (qe) increased, indicating that HCrO4− and Cr2O72− first occupied high-energy adsorption sites and then the low-energy adsorption sites. Reduction of Cr(VI) to Cr(III) was identified as significant in the elimination of Cr(VI). These findings offer new insights into the reusability behavior and interaction mechanisms of adsorbents during Cr(VI) elimination from wastewater.

Biochar supported nanoscale zerovalent iron-calcium alginate composite for simultaneous removal of Mn(II) and Cr(VI) from wastewater: Sorption performance and mechanisms

Heavy metal pollution in water caused by industrial activities has become a global environmental issue. Among them, manganese mining and smelting activities have caused the combined pollution of Cr(VI) and Mn(II) in water, posing a serious ecotoxicological risk to ecological environments and human health. To efficiently remove Cr(VI) and Mn(II) from wastewater, a novel biochar supported nanoscale zerovalent iron-calcium alginate composite (CA/nZVI/RSBC) was synthesized by liquid-phase reduction and calcium alginate embedding methods. The adsorption performance and mechanisms of Cr(VI) and Mn(II) by CA/nZVI/RSBC were investigated. The maximum adsorption capacities of Cr(VI) and Mn(II) onto CA/nZVI/RSBC fitted by the Langmuir model were 5.38 and 39.78 mg/g, respectively, which were much higher than the pristine biochar. The iron release from CA/nZVI/RSBC was comparatively lower than that of nZVI/RSBC. Mn(II) presence enhanced the reduction of Cr(VI) by CA/nZVI/RSBC. The results of XRD, XPS, and site energy distribution analysis indicated that redox was the predominant mechanism of Cr(VI) adsorption, while electrostatic attraction dominated Mn(II) adsorption. This study provides a novel alternative way for the simultaneous removal of Cr(VI) and Mn(II) in wastewater.

Customization, structural synthesis, and adsorption mechanism of lanthanide-dotted bio-based carbon

Overcoming the 'soft nature' of bio-based porous carbon materials (BPCM) has become a hot topic in the biochar field; hence the emphasis is on developing a new "powerful" structure for functional BPCM. This work utilizes f-orbital lanthanide elements to enhance the pore walls and fabricate successfully functionalized biochar (magnetically lanthanum-dot chitosan-biobased materials, MCS@La2O2CO3). The ultrastructure of the MCS@La2O2CO3 was characterized, and adsorption mechanisms were explored. The Site Energy Distribution Theory (SEDT) addressed to elucidate reactions and energy processes. The results indicate that MCS@ La2O2CO3 has a high surface area of 1587.88 m2·g−1 and magnetization value of 16.560 emu·g−1. Within 60 min, the functionalized MCS@La2O2CO3 exhibited exceptional adsorption capacity by absorbing over 200 mg·g−1 of various types of UV-filter pollutants, surpassing the majority of other BPCM. The Adsorption Coexistence Equation (MACE) was constructed to explain the monolayer-multilayer adsorption mechanism. The SEDT analysis further defines that the MCS@ La2O2CO3 structure is short-range disordered amorphous and exhibits high-energy selectivity, which is positively correlated with temperature. This work enables the omnidirectional enhancement of tailored biobased adsorbents for the depollution of UV-filter-contaminated water.

Unleashing the dye adsorption potential of polyaminoimide homopolymer: DFT, statistical physics, site energy and pore size distribution analyses

The efficient removal of Congo Red (CR) dye from aqueous solutions is an important issue in environmental protection. This study presents the synthesis and optimization of a polyaminoimide homopolymer (PHP) adsorbent for the removal of CR dye. To optimize the synthesis of PHP, ten different compositions of maleic anhydride and ethylene diamine were tested, with PHP3 demonstrating the highest efficacy. The adsorption process was further enhanced by optimizing pH, temperature, adsorbent dose, and initial dye concentration. Isotherm and kinetic studies revealed that the Langmuir-Freundlich model and the pseudo-second-order kinetics best described the adsorption process. Moreover, PHP3 demonstrated significantly greater selectivity for CR compared to Synozol yellow, and Sulfasalazine. Advanced statistical models were used to analyze the adsorption data, and the single-layer model with single energy (M1) being the most suitable, suggesting that CR molecules were adsorbed onto PHP3 in a perpendicular position through a multimolecular process, the adsorption process is physical, endothermic, spontaneous and specific surface area of PHP3 increased from 54.31 to 115.74 m2 g−1 as temperature rose from 288 to 318 K. Site energy distribution and pore size distribution studies showed that PHP3 has a heterogeneous energy distribution on its surface, and that the adsorption of CR dye primarily takes place in the macropores of PHP3. Density Functional Theory analysis indicated that PHP3 has electron-rich amine groups that can interact with electron-deficient sulfonate groups in CR, while electron-poor amide groups in the polymer can interact with the electron-rich azo group in Congo Red. It also shows that the presence of NaF, Na2SO4, and KCl salts did not significantly affect the CR adsorption, indicating the potential affinity/selectivity of PHP3 towards CR dye. The findings suggest that PHP3 could be an effective and promising adsorbent for industrial applications in wastewater treatment.

Physicochemical and adsorptive properties of biochar derived from municipal sludge: sulfamethoxazole adsorption and underlying mechanism

Municipal sludge waste could be transformed into useful biochar through pyrolysis process. In this study, municipal sludge-derived biochar (SBC) was successfully synthesized via the one-pot pyrolysis method, and the yield of sludge biochar gradually decreased with the pyrolysis temperature increased from 300°C to 800°C. The sludge biochar exhibited an alkaline surface due to the gradual accumulation of ash and the formation of carbonate and organic anion during high-temperature pyrolysis process. Moreover, the prepared samples were analyzed by different characterization techniques including BET, SEM, and XPS. Adsorption experiments using the optimized biochar sample of SBC800 resulted in a 95% sulfamethoxazole (SMX) removal efficiency and the maximum adsorption capacity of 7033.4 mg/kg, which was 47.5 times higher than that of SBC300. The adsorption process of SBC800 for SMX was more in line with the Freundlich and D-A isotherm model, the whole process was an exothermic reaction. SBC800 could effectively remove SMX through pore filling effect, electrostatic attraction, hydrogen bonding, hydrophobic effect, and π-π EDA interaction. Site energy distribution analysis showed that SMX preferentially occupied the high-energy adsorption site of SBC800, and then gradually diffused to the low-energy adsorption site. This study proposed a sustainable method for recycling municipal sludge for organic pollutant removal.

Modeling of heterogeneous site energy distributions in precipitate nucleation

The simulation of heat changes resulting from phase transitions can help to interpret differential scanning calorimetry (DSC) measurements, e.g. of metallic alloy systems in which multiple reactions overlap during non-isothermal heat treatments. So far, simulated DSC curves mostly exhibit sharp reaction peaks as commonly just one mean energy value for a certain type of nucleation site is assumed. This work proposes an efficient model for treating heterogeneous nucleation site energy variations within the framework of classical nucleation theory (CNT). The site energies are assumed to vary according to a Rayleigh distribution and a scaling function. The effect on the nucleation behavior of precipitates is studied. A consideration of the distribution of heterogeneous site energies has the potential to significantly smoothen the numerical treatment of precipitation processes compared to the non-distributed case. The comparison to previously published simulations of DSC curves during the cooling of an AA6005 aluminum alloy demonstrates the advantages of this extension, especially for slow cooling rates.

Comparative study of in-situ formation process of Mg-Al layered double hydroxides though two pathways to remove Cr(VI) and As(V) from wastewater

The method of direct synthesis of layered double hydroxide (LDHs) in wastewater has attracted wide attention, but the formation process and removal mechanism are still unclear. In this study, two different paths of alkali solution (NaOH) dropped to salt solution (Mg2+/Al3+) (A-S process) and salt solution dropped to alkali solution (S-A process) were proposed to directly synthesize LDHs in wastewater and remove contaminants Cr(VI)/As(V) simultaneously. In A-S process, the formation of LDHs could be divided into three stages: initial formation of amorphous Al(OH)3, crystal phase transformation, and the complete formation of LDHs crystal. There was a gradual incorporation of Mg into Al(OH)3, and the removal of Cr(VI)/As(V) significantly increased upon the formation of LDHs structure. However, in S-A process, the formation of LDHs primarily involved crystal structure optimization. The layered structure was constantly growing and optimizing, accompanied by the removal of Cr(VI)/As(V). The Competition removal experiment of Cr(VI)/As(V) indicated that As(V) preferentially possess active sites and occupied more high-energy sites analyzed by molecular simulation and site energy distribution theory. The experimental investigation of co-existing ions, pH and recycle experiment for practical performance were also examined and demonstrated a high stability and a good recyclability.