Evaluating the Suitability of Linear and Nonlinear Regression Approaches for the Langmuir Adsorption Model as Applied toward Biomass-Based Adsorbents: Testing Residuals and Assessing Model Validity.

Regression analysis is a powerful tool in adsorption studies. Researchers often favor linear regression for its simplicity when fitting isotherm models, such as the Langmuir equation. Validating regression assumptions is crucial to ensure that the model accurately represents the data and allows appropriate inferences. This study provides a detailed examination of assumption checking in the context of adsorption studies while simultaneously evaluating the robustness of linear regression methods for fitting the Langmuir equation to isotherm data from 2,4-dichlorophenol (DCP) adsorption onto various biomass-based adsorbents and activated carbon. Different linearized Langmuir equations (Hanes-Woolf, Lineweaver-Burk, Eadie-Hofstee, and Scatchard) were compared to nonlinear regression, and each method was validated by rigorous residual checking. This included visual plots of residuals as well as statistical tests, including the Durbin-Watson test for autocorrelation (independence), the Shapiro-Wilk test for normality, and the White test for homoscedasticity. Key findings indicate that the Hanes-Woolf (type 1) and Lineweaver-Burk (type 2) linearizations were the best for most biomass adsorbents studied and that Eadie-Hofstee (type 3) and Scatchard (type 4) were generally invalid due to the negative parameters or assumption violations. For activated carbon, all linearization methods were unsuitable due to independence violations. In the case of nonlinear regression, there were no major assumption violations for all of the adsorbents. Symbolic regression identified the Langmuir equation only for activated carbon (AC). This study revealed shortcomings in relying solely on linearized Langmuir models. A proposed workflow recommends using nonlinear or weighted nonlinear regression, starting with Hanes-Woolf or Lineweaver-Burk linearization results as initial values for parameter estimation. If assumptions remain violated with nonlinear techniques, novel methods such as symbolic regression should be employed. This advanced regression technique can improve adsorption models' accuracy and predictive behavior without the stringent need for assumption checking. Symbolic regression can also aid in understanding mechanisms of novel adsorbents.

FeS2 deposited on 3D-printed carbon microlattices as free-standing electrodes for lithium-ion batteries.

We introduce free-standing FeS2/carbon microlattice composites as electrodes for lithium-ion batteries through 3D printing. The computer-aided design allows for any shape. The microlattice features aligned microchannels, promoting ion transfer, while the carbon skeleton facilitates electron transfer. Overall, this study shows 3D printing is highly promising in advancing sustainable energy applications.

A review of PFAS adsorption from aqueous solutions: Current approaches, engineering applications, challenges, and opportunities.

Per- and polyfluoroalkyl substances (PFAS) have drawn great attention due to their wide distribution in water bodies and toxicity to human beings. Adsorption is considered as an efficient treatment technique for meeting the increasingly stringent environmental and health standards for PFAS. This paper systematically reviewed the current approaches of PFAS adsorption using different adsorbents from drinking water as well as synthetic and real wastewater. Adsorbents with large mesopores and high specific surface area adsorb PFAS faster, their adsorption capacities are higher, and the adsorption process are usually more effective under low pH conditions. PFAS adsorption mechanisms mainly include electrostatic attraction, hydrophobic interaction, anion exchange, and ligand exchange. Various adsorbents show promising performances but challenges such as requirements of organic solvents in regeneration, low adsorption selectivity, and complicated adsorbent preparations should be addressed before large scale implementation. Moreover, the aid of decision-making tools including response surface methodology (RSM), techno-economic assessment (TEA), life cycle assessment (LCA), and multi criteria decision analysis (MCDA) were discussed for engineering applications. The use of these tools is highly recommended prior to scale-up to determine if the specific adsorption process is economically feasible and sustainable. This critical review presented insights into the most fundamental aspects of PFAS adsorption that would be helpful to the development of effective adsorbents for the removal of PFAS in future studies and provide opportunities for large-scale engineering applications.

Formulation of a Simulated Wastewater Influent Composition for Use in the Research of Technologies for Managing Wastewaters Generated during Manned Long-Term Space Exploration and Other Similar Situations-Literature-Based Composition Development.

The prospect of humans inhabiting planetary bodies is gaining interest among research and development communities, with the moon being considered as a transitory base camp and Mars the next planet humans will inhabit. NASA's Mission to Mars program is set to have humans inhabiting Mars within on-planet space camps by the Year 2030, which has tremendously increased research and development for space exploration-including research oriented toward human life support in long-term planetary lodging camps. The sustenance of human life on Mars will not be trivial due to the unavailability of an appropriate atmosphere and usable water. This situation requires a self-sustaining human life support system that can provide the basic needs such are breathable air, potable water, food, and energy. The feasibility of sending a payload with resources adequate to support long-term human inhabitation is not reasonable, which means every resource within a Mars space camp is valuable, including human-produced wastes. A biorefinery system that treats wastewater and can also produce valuable products such as oxygen, food, and energy offers a form of circular utilization of valuable resources. To conduct research for such systems requires a wastewater influent that is representative of the wastewater to be generated by the space crew within this isolated, confined environment, which is different from what is generated on Earth due to limited variability in diet, human activity, and lifestyle in this confined area. Collection of actual wastewater influent from an isolated environment supporting humans is challenging. Additionally, to ensure a safe working environment in the laboratory and avoid the imposed threat of handling actual human feces, the proposed synthetic, non-human feces containing wastewater influent formulation offers an easy-to-produce and safer-to-handle option. This paper reviews several synthetic wastewater compositions that have been formulated for space exploration purposes. None of the formulations were found to be realistic nor adequate for a space-camp-type scenario. Thus, the formulation of a synthetic wastewater for simulating a wastewater influent from a human space-based camp is proposed in this paper. In addition, the physical, chemical, and biodegradation characteristics of the final formulation designed are presented to illustrate the value of the proposed influent formulation.

Removal of perfluorooctanoic acid via polyethyleneimine modified graphene oxide: Effects of water matrices and understanding mechanisms.

This research aimed to evaluate the adsorption behaviors and mechanisms of perfluorooctanoic acid (PFOA) onto polyethyleneimine modified graphene oxide (GO-PEI) from aqueous solutions. The adsorption capacity was significantly improved by doping polyethyleneimine (PEI) onto graphene oxide (GO). The Brunauer-Emmett-Teller (BET) isotherm model was considered as the best isotherm model in describing the PFOA adsorption onto GO-PEI3 (wPEI/wGO = 3). GO-PEI3 exhibited high adsorption capacity (qe = 368.2 mg/g, calculated from BET isotherm model) and excellent stability. The maximum monolayer amount of PFOA adsorption onto GO-PEI3 (qm = 231.2 mg/g) was successfully evaluated. The calculated saturated concentration (Cs = 169.9 mg/L) of PFOA on GO-PEI3 closely agrees with its critical micelle concentration (CMC = 157.0 mg/L), suggesting the formation of multilayer hemi-micelles or micelles PFOA structures on the surface of GO-PEI3. PFOA adsorption onto GO-PEI3 was inhibited by several factors including: the presence of humic acid (HA) by competing with the adsorption sites, background salts through the double-layer compression effect, and the competition from soluble ions for the amine or amide functional groups on GO-PEI3. Finally, both the FT-IR and XPS results confirmed that the adsorption of PFOA onto GO-PEI3 was through electrostatic attraction and hydrophobic interaction (physical adsorption), but not chemical adsorption. This work provides fundamental knowledge both in understanding the adsorption behavior through the BET isotherm model and in developing a stable adsorbent for PFOA adsorption. In addition, the findings highlight the potential of PFOA remediation from wastewater systems using GO-PEI in engineering applications.

Surface-bound hydroxyl radical-dominated degradation of sulfamethoxazole in the amorphous FeOOH/ peroxymonosulfate system: The key role of amorphous structure enhancing electron transfer.

In this study, activation of peroxymonosulfate (PMS) by amorphous FeOOH to degrade sulfamethoxazole (SMX) was investigated. The amorphous FeOOH showed a better performance in the decomposition of PMS and the degradation of SMX than the crystallized α-FeOOH and ß-FeOOH. The quenching experiments and EPR measurements suggested that the mechanism of PMS activation by amorphous FeOOH was mainly the surface-bound radicals (●OH and SO4●-). Basically, the surface-bound ●OH radicals were the dominate reactive oxide species in this system, which were mainly generated via the decomposition of amorphous FeOOH-PMS complexes. The degradation of SMX was significantly inhibited with the presence of H2PO4-, and this adverse impact was negligibly affected by the increase of H2PO4- concentration, implying that the inhibition of SMX degradation was caused by competitive adsorption. Consequently, the Fe-OH bonds on the amorphous FeOOH were proposed as the reactive sites for forming amorphous FeOOH-PMS complexes. Besides, the amorphous FeOOH showed a better performance in the degradation of SMX in the acid conditions than that in the base conditions due to the surface charge of amorphous FeOOH. More importantly, the reduction efficiency of Fe(III) was significantly enhanced due to the excellent conductivity of amorphous FeOOH.

Land use, hydrology, and climate influence water quality of China's largest river.

Influences of multiple environmental factors on water quality patterns is less studied in large rivers. Landscape analysis, multiple statistical methods, and the water quality index (WQI) were used to detect water quality patterns and influencing factors in China's largest river, the Yangtze River. Compared with the dry season, the wet season had significantly higher total phosphorus (TP), chemical oxygen demand (COD), total suspended solids (TSS), and turbidity (TUR). The WQI indicated "Moderate" and "Good" water quality in the wet and dry seasons, respectively. Compared with other sites, the upper reach sites that immediately downstream of the Three Gorges Dam had lower TP, TN, TSS and TUR in both seasons, and had lower and higher water temperature in the wet and dry seasons, respectively. Water quality patterns were mainly driven by heterogeneity in land use (i.e., wetland, cropland, and urban land), hydrology (i.e., water flow, water level), and climate (i.e., rainfall, air temperature). Water quality in the wet season was primarily driven by land use while the joint effect of land use and hydrology primarily drove in the dry season. Decision-makers and regulators of large river basin management may need to develop programs that consider influences from both human and natural drivers for water quality conservation.

Insight into the activation mechanisms of biochar by boric acid and its application for the removal of sulfamethoxazole.

Sulfamethoxazole (SMX) is frequently detected in the environment and causes a huge threaten to human health. Biochar (BC) is a metal-free adsorbent and generally exhibits a good adsorption capacity for SMX. However, the current activated methods usually result in the high energy consumption and low yield of the biochar. In this study, biochar was activated by boric acid under limited oxygen condition. The yield of biochar was increased by 103% after the activated by boric acid. The specific surface area of BC was significantly increased from 766.6 m2·g-1 to 1190.6 m2·g-1. The intensity of the (111) diamond peak of B-BC was higher than that of BC, suggesting that boric acid affected the surface pyrolysis temperature of biochar. The proposed roles of boric acid in the activation process were to: 1) enhance the generation of micropores during the pyrolysis process; 2) improve the yield of biochar via the transformation pathways of C-corresponding bonds and physical blocking. The boric acid activated biochar (B-BC) had a higher adsorption capacity for SMX than BC under the various aqueous conditions. Hence, boric acid activated biochar is a promising porous adsorbent to enhance the removal of SMX and achieve practical application.

Enhanced adsorption of perfluorooctanoate (PFOA) onto low oxygen content ordered mesoporous carbon (OMC): Adsorption behaviors and mechanisms.

The pollution of perfluorooctanoic acid (PFOA) in water bodies has been a serious threat to environment and human health. Ordered mesoporous carbons (OMCs) with different oxygen contents were prepared and first used for adsorbing PFOA from aqueous solutions. The OMC-900 with a lower oxygen content has a higher PFOA adsorption capacity than the oxygen-rich OMC-700. OMCs require a much shorter time to reach the adsorption equilibrium comparing with other adsorbents reported in literature. The mesopores play an important role in this rapid adsorption kinetics. The pseudo-second-order model better fitted the kinetic data. The multilayers adsorption was proposed for the adsorption of PFOA onto OMCs since the Freundlich isotherm model fits the experimental data well. The micelle or hemi-micelle structures may be formed during the adsorption. Various background salts showed a positive effect on PFOA adsorption due to the salting-out and divalent bridge effects. The humic acid can lead to a discernible reduction in PFOA adsorption by competing for adsorption sites on OMCs. The hydrophobic interaction and electrostatic interaction adsorption mechanisms were proposed and verified by the adsorption data. The high adsorption capacity and fast adsorption kinetics of the OMC make it a potential adsorbent for PFOA removal in engineering applications.

Synergistic adsorption and degradation of sulfamethoxazole from synthetic urine by hickory-sawdust-derived biochar: The critical role of the aromatic structure.

This study investigated the adsorptive removal and subsequent degradation of sulfamethoxazole (SMX) from a synthetic urine by biochar (BC). The BCs used in this study were prepared using two different feedstocks with different temperatures. Element analysis and Fourier transform infrared spectroscopy (FTIR) results suggested that the aromaticity of one of the BCs, 700HSBC was significantly different from the 700PSBC although both of them were prepared at the same temperature (700 °C) with similar pore size distributions and specific surface areas. Due to the presence of abundant aromatic structures, 700HSBC showed a higher SMX uptake than 700PSBC, suggesting that the π-π interaction was the main adsorption mechanism. The removal of SMX from the urine was significantly enhanced by adding hydrogen peroxide to the 700HSBC. The carbonate radicals degradation of SMX mechanism was proposed and verified. With 700HSBC having abundant aromatic structures acting as π-electron donors, it could be an efficient activator for peroxymonocarbonate (HCO4-) to generate carbonate radicals. Hence, it could be concluded that the aromatic structures on BCs play a key role in both of the adsorption and hydrogen peroxide degradation of the SMX resulting in its removal from urine.

Enhanced adsorption of resorcinol onto phosphate functionalized graphene oxide synthesized via Arbuzov Reaction: A proposed mechanism of hydrogen bonding and π-π interactions.

Phosphate functionalized graphene oxide (PGO) was successfully prepared by Arbuzov reaction and employed for adsorption of resorcinol from an aqueous phase. The phosphate functional groups were successfully incorporated onto the PGO surface by the formation of P-C bonds as identified by the analysis of FTIR and XPS spectra. The evaluation of adsorption capacity of resorcinol onto PGO exhibited significant improvement of resorcinol removal, achieving an adsorption capacity of 50.25 mg/g in the pH range of 4-7 which was 15 times higher than pristine graphene oxide. The addition of 2.4 M and 5 M NaCl in the adsorption system significantly increased the adsorption capacity towards resorcinol from 50.25 mg/g to 82.10 mg/g and 128.10 mg/g, respectively. Based on kinetics and adsorption isotherm studies, Pseudo-First-Order and Langmuir model are the best model to describe the adsorption process indicating that the adsorption is dominantly controlled by physisorption. The thermodynamic analysis suggested that the adsorption process was the favorable, spontaneous, and endothermic process. Besides, the interplay of hydrogen bonding and π-π interactions is proposed to be the governing physisorption mechanism. The outstanding reusability and better adsorption performance make PGO a promising adsorbent for environmental remediation of resorcinol.

A comparative study for phosphate adsorption on amorphous FeOOH and goethite (α-FeOOH): An investigation of relationship between the surface chemistry and structure.

Eutrophication is generally caused by excess nitrogen and phosphorus being released into surface waters by runoff. Developing adsorbents for adsorbing phosphate within soil buffer zones and/or water treatment columns may be effective methods to mitigate this problem. In this study, an amorphous FeOOH (AF) and a well-crystallized α-FeOOH (CF) was formulated to compare phosphate adsorption behavior. The physicochemical properties between these species showed significant differences in morphology, crystallization, zeta potential, and specific surface area. The AF exhibited higher phosphate uptake than CF. X-ray photoelectron spectroscopy (XPS) verified that the hydroxyl groups within AF were 13.28% higher than that in CF. The triply coordinated hydroxyl groups (µ3-OH) associated with AF and CF appeared at different positions as shown in the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses, confirming that AF contains more adsorption reactive sites (µ3-OH). Mechanisms for monodentate formations and a stable six-member ring structure were proposed. The X-ray absorption near the edge structure (XANES) and XPS results suggested that the iron valence in AF was dominated by Fe (III). XANES also demonstrated that the amorphous structure found in the AF was caused by the disordered tetrahedron and octahedron alignments, leading to a higher phosphate adsorption.

Goethite dispersed corn straw-derived biochar for phosphate recovery from synthetic urine and its potential as a slow-release fertilizer.

In this study, goethiete (α-FeOOH) -biochar (BC) composites were successfully developed from a co-precipitation reaction under alkaline conditions (pH = 11.93) and used as the adsorbent for phosphate recovery from urine. The morphology and crystallinity of α-FeOOH-BC composites were characterized by scanning electron microscopy and X-ray diffraction. α-FeOOH loaded BC was found to be amorphous. This may be caused by the Si residue in BC. The Elovich model and the Langmuir model fit better to the kinetic and isotherm results of α-FeOOH-600BC, respectively, indicating that phosphate adsorption is mainly a chemisorption and monolayer adsorption process. The α-FeOOH-600BC with amorphous structure showed higher adsorption capacity than crystalline α-FeOOH, and the maximum phosphate sorption capacity reached 57.39 mg g-1. Additionally, the extractable phosphate of this material was approximately 967.5 mg P·kg-1 suggesting the α-FeOOH-600BC after adsorption could be a promising alternative as a slow-phosphate-release fertilizer. Fourier-transform infrared and X-ray induced photoelectron spectroscopy results showed that the active sites of the adsorption of phosphate were the Fe-OH bonds that formed inner-sphere complexes (Fe-O-P).

Uniform Mesoporous Amorphous Cobalt-Inherent Silicon Oxide as a Highly Active Heterogeneous Catalyst in the Activation of Peroxymonosulfate for Rapid Oxidation of 2,4-Dichlorophenol: The Important Role of Inherent Cobalt in the Catalytic Mechanism.

Amorphous cobalt-inherent silicon oxide (Co-SiOx) was synthesized for the first time and employed as a highly active catalyst in the activation of peroxymonosulfate (PMS) for the rapid oxidation of 2,4-dichlorophenol (2,4-DCP). The characterization results revealed that the 0.15Co-SiOx possessed a high specific surface area of 607.95 m2/g with a uniform mesoporous structure (24.33 nm). The X-ray diffraction patterns indicate that the substituted cobalt atoms enlarge the unit cell parameter of the original SiO2, and the selected area electron diffraction pattern confirmed the amorphous nature of Co-SiOx. More bulk oxygen vacancies (Ov) existing in the Co-SiOx were identified to be one of the primary contributors to the significantly enhanced catalytic activation of PMS. The cobalt substitution both creates and stabilizes the surficial Ov and forms the adequately active Co(II)-Ov pairs which engine the electron transfer process during the catalytic activities. The active Co(II)-Ov pairs weaken the average electronegativity of Co/Si and Co/O sites, resulting in the prevalent changes in final state energy, which is the main driving cause of the binding energy shifts in the X-ray photoelectron spectroscopy (XPS) spectra of Si and O among all samples. The increase of the relative proportion of Co(III) in the spent Co-SiOx probably causes the binding energy shifts of the Co XPS spectrum compared to that of the Co-SiOx. The amorphous Co-SiOx outperforms stable and quick 2,4-DCP degradation, achieving a much higher kinetic rate of 0.7139 min-1 at pH = 7.02 than others via sulfate radical advanced oxidation processes (AOPs), photo-Fenton AOPs, H2O2 reagent AOPs, and other AOP approaches. The efficient degradation performance makes the amorphous Co-SiOx as a promising catalyst in removing 2,4-DCP or organic-rich pollutants.

A holistic assessment of water quality condition and spatiotemporal patterns in impounded lakes along the eastern route of China's South-to-North water diversion project.

Water quality is one of the key determinants for assessing effectiveness and success of water diversions, but rarely studied at a spatial scale that crosses large river basins. Multiple statistical methods and the water quality index (WQI) were used to assess overall condition and detect spatiotemporal patterns of water quality in a series of impounded lakes along the Eastern Route of China's South-to-North Water Diversion Project. Principal components analysis and analysis of variances identified three groups with distinct water quality characteristics: upstream Gaoyou Lake and Hongze Lake showing relatively higher nutrients, turbidity, and total suspended solids; downstream Dongping lake and Donghu Lake showing higher conductivity, total hardness, and chloride; and Luoma Lake and Nansi Lake intermediate between the two former groups. The WQI indicated overall "Good" water quality with an improving trend from upstream to downstream lakes. The upstream Gaoyou Lake had over 55% of the monitoring sites with "Moderate" water quality in all the seasons. Management should focus on preventing high nitrogen, phosphorus, turbidity, and total suspended solids in upstream lakes, high chloride in downstream lakes, high nitrogen during water diversion seasons, and high phosphorus during non-water diversion seasons. These findings greatly improved our understanding of the spatiotemporal water quality patterns of the impounded lakes, and can be used to develop water quality management strategies. This study exemplifies a methodology for investigating and securing water quality for inter-basin water transfer projects.

Analysis and Risk Assessment of Organic Pollutants in Surface Water from Xujiahe Basin, China.

In this study, organic compounds were screened in surface water collected from Xujiahe basin, China by gas chromatography-mass spectrometry (GC-MS). A total of 51 compounds were identified including 14 organochlorine pesticides (OCPs), 9 organophosphorus pesticides (OPs), 16 polycyclic aromatic hydrocarbons (PAHs) and 12 chlorobenzene (CBs). The concentrations of OCPs, PAHs and CBs were generally low. The concentrations of OCPs in Xujiahe reservoir ranged from N.D. to 35.6 ng/L, the concentrations of PAHs ranged from N.D. to 19.8 ng/L and the concentrations of CBs ranged from 10.3 to 124.6 ng/L. The Ecological Structure Activity Relationships (ECOSAR) model was employed to directly predict the integrated toxicity indexes of 51 organic pollutants. The risk quotient (RQ) values of most of the organic compounds in the water samples were acceptable for their ecological risk.

The use of artificial neural network (ANN) for modeling adsorption of sunset yellow onto neodymium modified ordered mesoporous carbon.

Discharging coloring products in water bodies has degraded water quality irreversibly over the past several decades. Order mesoporous carbon (OMC) was modified by embedding neodymium(III) chloride on the surface of OMC to enhance the adsorptive removal towards these contaminants. This paper represents an artificial neural network (ANN) based approach for modeling the adsorption process of sunset yellow onto neodymium modified OMC (OMC-Nd) in batch adsorption experiments. Neodymium modified OMC was characterized using N2 adsorption-desorption isotherm, TEM micrographs, FT-IR and XPS spectra analysis techniques. 2.5 wt% Nd loaded OMC was selected as the final adsorbent for further experiments because OMC-2.5Nd showed highest removal efficiency of 93%. The ANN model was trained and validated with the adsorption experiments data where initial concentration, reaction time, and adsorbent dosage were selected as the variables for the batch study, whereas the removal efficiency was considered as the output. The ANN model was first developed using a three-layer back propagation network with the optimum structure of 3-6-1. The model employed tangent sigmoid transfer function as input in the hidden layer whereas a linear transfer function was used in the output layer. The comparison between modeled data and experimental data provided high degree of correlation (R2 = 0.9832) which indicated the applicability of ANN model for describing the adsorption process with reasonable accuracy.

Enhanced Pb(II) adsorption onto functionalized ordered mesoporous carbon (OMC) from aqueous solutions: the important role of surface property and adsorption mechanism.

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO3 and H3PO4 to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pHpzc, the main Pb(II) existing species of Pb(II) and Pb(OH)+ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

The effects of carbon disulfide driven functionalization on graphene oxide for enhanced Pb(II) adsorption: Investigation of adsorption mechanism.

The surface properties of graphene oxide (GO) have been identified as the key effects on the adsorption of Pb(II) from aqueous solutions in this study. This study reveals the effect of the surface reactivity of GO via Carbon Disulfide (CS2) functionalization for Pb(II) adsorption. After successfully preparing CS2 functionalized GO (GOCS), the specific techniques were applied to investigate Pb(II) adsorption onto GOCS. Results indicated that the new sulfur-containing functional groups incorporated onto GOCS significantly enhanced Pb(II) adsorption capacity on GOCS than that of GO, achieving an improvement of 31% in maximum adsorption capacity increasing from 292.8 to 383.4 mg g-1. The equilibrium adsorption capacity for GOCS was 280.2 mg g-1 having an improvement of 83.2% over that of 152.97 mg g-1 for GO at the same initial concentration of 150 mg L-1 under the optimal pH of 5.7. Moreover, the results of adsorption experiments showed an excellent fit to the Langmuir and Pseudo-Second-Order models indicating the monolayer and chemical adsorption, respectively. The mechanism for Pb(II) adsorption on GOCS was proposed as the coordination, electrostatic interactions, cation-pi interactions, and Lewis acid-base interactions. The regeneration study showed that GOCS had an appreciable reusability for Pb(II) adsorption with the adsorption capacity of 208.92 mg g-1 after five regeneration cycles. In summary, GOCS has been proved to be a novel, useful, and potentially economic adsorbent for the high-efficiency removal of Pb(II) from aqueous solutions.

Modeling mass transfer for adsorptive removal of Pb(II) onto phosphate modified ordered mesoporous carbon (OMC).

Phosphate modified ordered mesoporous carbon (MOMC-NP) has been synthesized and proven to be an effective adsorbent for Pb(II) removal from aqueous solutions. However, the key application components of the mass transfer operations and diffusion coefficient have not been determined. In this study, a modified Finite Bath Diffusion Control Model was mathematically developed containing a constant related to the radius of the adsorbent particle and the fractional attainment of adsorption. The adsorption experiments were conducted under various initial Pb(II) concentrations ranging from 60 mg L-1 to 100 mg L-1. The results suggested that the modified Finite Bath Diffusion Control Model was more applicable to the experimental data than the original Finite Bath Diffusion Control Model. The average value of the diffusion coefficient (λD¯) obtained from the modified finite bath diffusion control model was 1.63 × 10-2 cm2 s-1 indicating the effective diffusivity in the adsorption of Pb(II) on MOMC-NP. Overall, the modified Finite Bath Diffusion Control Model exhibited the precise description and simulation of the mass transfer kinetics for Pb(II) adsorption onto MOMC-NP. Therefore, the modified Finite Bath Diffusion Control Model could be effectively used to investigate the mass transfer kinetics of the adsorption process.