Influence Of Solution pH Research Articles

An Investigation of the Batch Adsorption Capacity for the Removal of Phosphate from Wastewater Using Both Unmodified and Functional Nanoparticle-Modified Biochars

One of the most widely employed methods for adsorption is the utilization of biochar produced during pyrolysis. Biochar has attracted considerable attention due to its oxygen-containing functional groups and relatively high specific surface area. In alignment with the principles of cleaner production, the sludge generated from sewage treatment plants is typically classified as waste. However, it can be effectively repurposed as an adsorbent following pyrolysis and subsequent nanoparticle modification. This environmentally friendly approach presents an ecological alternative to conventional water treatment methods. The objective of this study is to evaluate the efficiency of batch adsorption for the removal of phosphate from wastewater using both unmodified and modified sewage sludge biochars (SSBs) that were produced at various temperatures (300 °C, 400 °C, 500 °C, and 600 °C) and modified with zero-valent iron nanoparticles (nZVI-SSB300, nZVI-SSB400, nZVI-SSB500, and nZVI-SSB600). The findings indicate that biochar modified with functional nanoparticles is a highly effective adsorbent for the removal of phosphate from wastewater. As demonstrated by the research results, the adsorption capacity of modified biochar is approximately 3 to 3.5 times greater than that of the unmodified variants. The phosphate removal efficiency with modified biochars was optimal with nZVI-SSB600. In experiments with a phosphate concentration (25 mg/L), the modified sorbent biochar exhibited an equilibrium adsorption capacity of 23.74 mg/g, translating to a phosphate removal efficiency of 60%. Under similar test conditions, at an initial phosphate concentration of 50 mg/L, the adsorption capacity improved to 25.67 mg/g (75% efficiency); at 75 mg/L, it reached 27.97 mg/g (80%); at 100 mg/L, it was 28.44 mg/g (85%); and at 125 mg/L, it achieved 29.48 mg/g (89%). The models confirmed the observed adsorption behavior, yielding a maximum phosphate adsorption capacity (qe) of 19.00 mg/g for the 600 °C pyrolysis of modified biochar at the primary phosphate concentration (25 mg/L). Furthermore, this study indicates that the influence of solution pH on phosphate adsorption remains stable and maximal (nZVI-SSB600, ranging from 16.87 to 20.46 mg/g) within the pH range of 3 to 8. On average, the modified biochar (nZVI-SSB) demonstrated 20 to 30% superior adsorption performance compared to the unmodified biochar (SSB). Additionally, significant differences were noted between various ambient temperatures, ranging from 5 °C to 25 °C. As the ambient temperature increased, the sorption capacity of the adsorbent exhibited a considerable improvement. With a primary concentration of phosphate (100 mg/g) at 5 °C, the adsorption capacity of nZVI-SSB600 was measured at 7.99 mg/g; this increased to 14.33 mg/g at 10 °C, 21.79 mg/g at 20 °C, and 28.44 mg/g at 25 °C. This research highlights the potential application of biochar in wastewater treatment for phosphate removal, simultaneously enabling the effective utilization of generated sewage sludge waste through pyrolysis and coating with zero-iron nanoparticles, resulting in a sustainable solution.

Turning properties of Ni/Al2O3 catalyst to improve catalytic ammonia decomposition for green hydrogen production: pH does matter!

In this study, the influence of solution pH (6.0–12.5) of the cation–anion double hydrolysis (CADH) method in the formation of Ni/Al2O3 catalyst and its catalytic performance for green hydrogen production NH3 decomposition was studied for the first time. The physicochemical properties of the prepared catalysts were systematically characterized by various analysis techniques. The results indicated that pH conditions significantly influenced both the structural properties and catalytic activity of the derived Ni/Al2O3 catalysts. The better catalytic activity for NH3 decomposition over catalysts prepared under high pH conditions (pH ≥ 10.0) is mainly due to the appropriate synergic effect of the interaction between Ni and Al2O3 support, large active Ni surface area, and suitable porosity, particle size, and basicity of the catalyst. The correlation analysis and density functional theory (DFT) calculations confirm that the percentage of surface metallic Ni plays a crucial role in controlling the catalytic activity of Ni/Al2O3 catalysts. The 40Ni/Al2O3 catalyst (Ni = 40 wt%) could achieve over 94.5 % NH3 conversion under the harsh reaction conditions of 600 °C and NH3 WHSV of 54000 mL/gcat./h, and that stably maintained for 200 h without any obvious deactivation. Overall, our work not only highlights the critical role of pH conditions in the CADH solution for cost-effective Ni/Al2O3 catalyst preparation but also proposes a promising strategy for developing a highly active, stable, and Ru-free catalyst for practical hydrogen production via NH3 decomposition.

PH dependence of reactive oxygen species generation and pollutant degradation in Fe(II)/O2/tripolyphosphate system

It has been reported that tripolyphosphate (TPP) can effectively enhance the activation of O2 by Fe(II) to remove organic pollutants in the environment. However, the influence of solution pH on the generation and conversion of reactive oxygen species (ROS) and their degradation of pollutants in the Fe(II)/O2/TPP system needs further investigation. In this study, we demonstrated that O2•– and •OH were the main ROS responsible for degradation in the system at different pH conditions, and their formation rates were calculated using a steady-state model. Experiments combined with density functional theory (DFT) calculations showed that the p-nitrophenol (PNP) degradation pathway in the Fe(II)/O2/TPP system is regulated by solution pH. Specifically, at pH = 3, the existence of Fe(II) in the solution is dominated by [Fe(II)(HTPP)2]2−, which leads to a rapid conversion from O2 and HO2• to generate •OH, and PNP is primarily oxidatively degraded. However, at pH = 5/7, [Fe(II)(TPP)2]4− is taking the lead with which O2•– is accumulated in the solution due to the slow conversion to •OH in this condition, and the PNP is mainly reductively degraded. This study proposes a new strategy to achieve the targeted oxidative/reductive removal of different types of pollutants by simply varying the solution pH in the Fe(II)/O2/TPP system.

Can minor aspects of sample preparation have major impacts on the reliability of analytical methods? A study for Br, Cl, F, I, and S in seafood

The interest in assessing the presence of some chemical elements in seafood, such as halogens and sulfur, has been increasing. In this study, a novel analytical method was developed, enabling the determination of Br, Cl, F, I, and S in a single analysis in shellfish (brown-mussel, Perna perna), common octopus (Octopus vulgaris), and fish (argentine hake, Merluccius hubbsi), using ion chromatography coupled to mass spectrometry (IC-MS). It was observed that sample pre-treatment by oven-drying at 100 °C can cause F losses by volatilization, compared to other drying methods, such as oven-drying at 60 °C and freeze-drying. Also, the pH of the digests is not the only factor affecting halogen stabilization after microwave-induced combustion (MIC), and other aspects must be considered, such as the concentration of the analytes and the absorbing solution composition. MIC provided suitable recoveries (92% to 108%) for all analytes using 250 mmol L-1 NH4OH as the absorbing solution when combined with IC-MS determination. The trueness of the proposed method was also evaluated by analyzing standard reference materials (SRMs NIST 1566a and 2976, oyster and mussel tissues). Results did not present statistical differences (Student’s t-test, confidence level of 95%) compared to the certified/reference values (agreements varying from 95% to 109% for all analytes). Analyte content (mass fraction) varied in a large range: 7 to 181 mg kg−1 for Br; 1,285 to 24,176 mg kg−1 for Cl; 5 to 34 mg kg−1 for F; < 3.3 to 7 mg kg−1 for I; and 7,917 to 17,409 mg kg−1 for S. The proposed method is a novel and reliable analytical tool and, at the same time, new insights on the influence of solution pH and drying method on the sample preparation step were provided.

Efficient ethidium bromide removal using sodium alginate/graphene oxide composite beads: Insights into adsorption mechanisms and performance

This study explores the efficacy of sodium alginate/graphene oxide (SA/GO) composite beads for ethidium bromide (EtBr) removal from aqueous solutions. GO was synthesized and crosslinked with SA to design composite beads, which were evaluated under various physicochemical conditions. Characterization techniques, including FESEM, TGA, XRD, and FTIR, were employed to analyze the beads before and after EtBr adsorption. Results demonstrated rapid EtBr adsorption onto SA/GO, following the Freundlich isotherm model with a maximum adsorption capacity of 2.97mmol g−1 (1171.05 mg g−1). The influence of solution pH and the negligible role of Br− ions suggested that electrostatic interaction was the primary mechanism for EtBr adsorption on SA/GO. XRD and FTIR analyses revealed that EtBr adsorption also occurred in the interlayer space of SA/GO beads, with the ethidium cations (Et+) entering this space in a horizontal or oblique (≥45°) orientation. The accumulation of Et+ within the interlayer space was estimated to form 1–6 basic inclined layers. SA/GO beads demonstrated promising characteristics for EtBr pollutant treatment, including low environmental impact, cost-effectiveness, rapid adsorption kinetics, and high removal efficiency. This study provides valuable insights into the adsorption mechanisms and performance of SA/GO beads, highlighting their potential for future field applications in the environmental remediation of EtBr contamination.

A novel potato peels waste β-cyclodextrin biocomposite for the efficient uptake of diuron and glyphosate herbicides.

A novel biocomposite (FPPW-β-CD) was prepared by a simple and sustainable method involving fine potato peel waste, β-cyclodextrin (β-CD), and green citric acid through the crosslinking reaction. The polymer was characterized using SEM, FTIR, XRD, TGA, and DSC analyses. The adsorbent performance was evaluated about the glyphosate and diuron adsorption from the aqueous solution. Pesticide removal was investigated regarding the influence of solution pH, temperature, and initial concentration of contaminants. Also, it highlights the main interactions involved in the adsorption phenomenon based on the pH effect and characteristics of adsorbent and adsorbate molecules. The maximum adsorption capacity values according to the Sips model were higher than 2000µgg-1. The pseudo-second-order and general-order models described the kinetic data well. Thermodynamic parameters indicated that pesticide removal was spontaneous and favorable. The magnitude of enthalpy variation values (27.37kJmol-1 and - 100.79kJmol-1) revealed that the glyphosate and diuron adsorption occurred through the physisorption and chemisorption, respectively. The novel biocomposite is a promising green adsorbent for the uptake of micropollutant pesticides in aqueous solutions at concentrations of µg L-1.

Adsorption behavior of heavy metals onto microplastics derived from conventional and biodegradable commercial plastic products

This study extensively explored the adsorption behavior of heavy metals (Pb+2, Ni+2, Cu+2, Zn+2, and Cd+2) onto microplastics (MPs). The particle sizes of MPs ranged from 0.149 to 0.25 mm. The microplastics were generated from commercial products manufactured from both conventional (polyethylene (PE) bottle, polystyrene (PS) spoon, and polyethylene terephthalate (PET) egg carton) and biodegradable (polylactic acid (PLA) spoon, and polylactic acid (PLA) egg carton) plastics. The study also considered the influence of solution pH on the adsorption capacity of heavy metals. Regarding the adsorption potential for Cu+2, the ranking was as follows: PLA-egg (1408 μg·g−1) > PLA-spoon (735 μg·g−1) > PE-bottle (315 μg·g−1) > PET-egg (283 μg·g−1) > PS-spoon (237 μg·g−1). PLA MPs showed the highest adsorption capacity due to the lower thermal stability and higher presence of surface oxygen functional groups. Moreover, the adsorption capacities of the five metals onto PLA-spoon and PLA-egg decreased in the following order: Pb (1785 μg·g−1) > Zn (1267 μg·g−1) > Cd (748 μg·g−1) > Cu (735 μg·g−1) > Ni (722 μg·g−1), and Pb (1520 μg·g−1) > Ni (1412 μg·g−1) > Cu (1408 μg·g−1) > Zn (1118 μg·g−1) > Cd (423 μg·g−1), respectively. The SEM-EDS, FTIR and XPS results demonstrated that surface oxygen-containing functional groups play an important role during the adsorption process. This study extended its analysis to quantify the metal content of the post-adsorption MPs, revealing uneven adsorption of heavy metals onto the MPs. This implies that the diversity of commercial plastic products may result in significant variations in their ability to adsorb heavy metals, underscoring the importance of effectively managing discarded commercial plastic products.

Fabrication of polydopamine/graphene oxide composite membranes for effective radionuclide removal

As the energy consumption surges in the past few decades, the utilization of reliable and cost-effective energy resources with minimum greenhouse gas emission is highly desirable, for which nuclear energy has gained intensive attention. The proper treatment of radioactive process water yet remains challenging, but is of vital importance due to its significant threats to environment and public health. In this work, a polydopamine/graphene oxide (PDA/GO) membrane was developed for radionuclide-contaminated water treatment. By the incorporation of PDA, the interlayer spacing of the GO membrane is regulated, as well as an improved anti-swelling property is achieved. At optimal preparation conditions, the PDA/GO has exhibited a high rejection of 99.9 % towards thorium ions with a satisfying water flux of 5.0 L·m−2h−1. Moreover, the influence of solution pH and thorium concentration on the membrane separation performance is studied. Results have indicated that the PDA/GO membrane presents a new promise for the treatment of radionuclide-contaminated water.

Performance of magnetic nanocomposite based on xanthan gum-grafted-poly(acrylamide) crosslinked by borax for the effective elimination of amoxicillin from aquatic environments

This study evaluated the effectiveness of using nanocomposite (NCs) of xanthan gum grafted polyacrylamide crosslinked Borax - iron oxide nanoparticle (XG-g-pAAm-CL-Borax-IONP) to remove the amoxicillin antibiotic (AMX) from an aquatic environment. To confirm the structural characteristics of the prepared XG-g-pAAm-CL-Borax-IONP NCs, unique characterization methods (XRD, FT-IR, FE-SEM, EDX, BET, TGA, Zeta, and VSM) were used. Adsorption experimental setups were performed with the influence of solution pH (4–9), the effect of adsorbent dose (0.003–0.02 g), the effect of contact time (5–45 min), and the effect of initial AMX concentration (50–400 mg/L) to achieve the most efficient adsorption conditions. Based on the Freundlich isotherm model, XG-g-pAAm-CL-Borax-IONP NCs provided the maximum AMX adsorption capacity of 1183.639 mg/g. This research on adsorption kinetics also established that the pseudo-second-order model (R2 = 0.991) is outstanding compatibility with the experimental results. AMX adsorption on the NCs may occur through intermolecular hydrogen bonding, diffusion, and trapping into the polymer network. Even after five cycles, these NCs still displayed the best performance. Based on these results, XG-g-pAAm-CL-Borax-IONP NCs may be a viable material for the purification of AMX from contaminated water.

An effective and comprehensive optimization strategy for preparing Ginkgo biloba leaf extract enriched in shikimic acid by macroporous resin column chromatography.

Previously reported preparation methods of Ginkgo biloba leaf extract (EGBL) have mainly focused on the enrichment of flavonoid glycosides (FG) and terpene trilactones (TT), which led to the underutilization of G. biloba leaves (GBL). To make full use of GBL, in this study, a comprehensive optimization strategy for preparing EGBL by macroporous resin column chromatography was proposed and applied to enrich FG, TT, and shikimic acid (SA) from GBL. Initially, the static adsorption and desorption were executed to select suitable resin. Then, the influences of solution pH were investigated by the static and dynamic adsorption. Subsequently, eight process parameters were systematically investigated via a definitive screening design (DSD). After verification experiments, scale-up enrichment was carried out, investigating the feasibility of the developed strategy for application on an industrial scale. It was found that XDA1 was the most appropriate adsorbent for the preparation of EGBL at solution pH 2.0. Furthermore, based on the constraints of the desired quality attributes, the optimized ranges of operating parameters were successfully acquired, and the verification experiments demonstrated the accuracy and reliability of using DSD to investigate the chromatography process for the preparation of EGBL. Finally, magnified experiments were successfully performed, obtaining the EGBL containing 26.54% FG, 8.96% TT, and 10.70% SA, which reached the SA level of EGB761, an international standard EGBL. The present study not only provided an efficient and convenient approach for the preparation of EGBL enriched in SA but also accelerated efforts to high-value utilization of GBL.

2D MoS2 nanosheets supported CoFe2O4 nanoparticles mediated persulfate activation for antibiotic removal

Advanced oxidation technology based on persulfate activation has caused extensive concern in the field of wastewater treatment. Nevertheless, this new technology is limited to the low catalytic efficiency and poor recovery of powder catalysts. Herein, we successfully synthesized MoS2 surface-supported CoFe2O4 nanoparticles composite catalyst employing a simple hydrothermal method. Compared with other systems, the performance of TC degradation was significantly improved by CoFe2O4/MoS2/PS system. Additionally, the influence of solution pH, catalyst dosage, PS dosage, and co-existing ions on the degradation process were studied. Both free radical (O2•−, •OH, SO4•−) and non-free radical (1O2) pathways coexisted in the catalytic degradation of TC on the account of radicals quenching experiments and electron spin resonance (ESR) technique. Additionally, the degradation pollutants were confirmed to display obvious decrease in toxicity based on microbial toxicology tests. Besides, CoFe2O4/MoS2 nanocomposite displays good magnetic recovery performance due to the introduction of CoFe2O4. In summary, this research provides a solid foundation for the application of magnetic CoFe2O4/MoS2 nanocomposite in the treatment of antibiotic wastewater.

Influence of solution pH on the dynamics of oxygen bubbles on the surface of TiO2-NTAs electrodes

The rise of concentration resistance caused by bubble growth is a key factor affecting the photoelectrochemical water splitting efficiency. In this research, we employed an electrochemical workstation, a synchronized measuring system, and a CCD camera to investigate the in-situ evolution of oxygen bubbles on the surfaces of TiO2-NTAs and C/TiO2-NTAs electrodes. The connection among the critical nucleation, growth and departure behavior of a single bubble on the photoanode surface and photocurrent curves at different solution pH (1–13) has been investigated. For TiO2-NTAs, it was found that strong alkalinity significantly reduces the voltage required for critical bubble nucleation. The photocurrent rises approximately 1.5 times when the control voltage is 0.10 V (vs. Ag/AgCl) by pH increasing from 1 to 13 and while the bubble evolution cycles decline by approximately 3.2 times. The photocurrent rises by 10.4 times compared with pH = 9 and by 7.3 times compared with pH = 13 when the control voltage is 0.71 V (vs. RHE), respectively. We also found that the oxygen bubble evolution of C/TiO2-NTAs is similar to TiO2-NTAs. When pH = 3–13, the average photocurrent of C/TiO2-NTAs electrode is higher than that of TiO2-NTAs, and the average bubble evolution cycles are lower than those of TiO2-NTAs at the same pH. According to the results, carbon films can rise the absorption capacity of TiO2-NTAs and significantly improve the effectiveness of photogenerated holes and electrons departure. Meanwhile, based on the oxygen bubble force balance model on the photoanode surface, the concentration Marangoni force rises with the increase of pH, which leads to the growth of bubble departure diameter. The outcomes demonstrate that oxygen bubbles on the photoanode surface can be successfully eliminated in strongly alkaline settings.

Design, Preparation, and Characterization of Polycaprolactone–Chitosan Nanofibers via Electrospinning Techniques for Efficient Methylene Blue Removal from Aqueous Solutions

The effective removal of organic dyes from aqueous solutions is of paramount importance in addressing environmental pollution challenges. Methylene blue (MB), a prevalent cationic dye in various industries, has raised concerns due to its persistence and potential adverse effects on ecosystems. This study explores the design, preparation, and characterization of Polycaprolactone–Chitosan (PCL–CH) nanofibers via electrospinning for the removal of MB. PCL, known for its biodegradability and mechanical properties, serves as the primary matrix, while chitosan (CH), with its biocompatibility and amino functionalities, offers enhanced adsorption potential. The electrospinning process yields nanofibers with tailored compositions and controlled morphology. The synthesized nanofibers are systematically characterized, encompassing structural analysis by Fourier transform infrared (FT–IR), spectroscopy, morphology, and composition assessment via Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS), zeta potential, as well as rheological behavior evaluation. The adsorption uptake of MB onto these nanofibers is investigated, considering the influence of solution pH and initial dye concentration. The results reveal significant enhancements in adsorption capacity, especially with the incorporation of CH, with the PCL–CH 30% nanofibers exhibiting outstanding performance. The pH-dependent behavior underscores the importance of environmental factors in the adsorption process, while higher dye concentrations provide a stronger driving force for adsorption. These findings position PCL–CH nanofibers as promising adsorbents for the efficient removal of MB and potentially other organic contaminants from aqueous solutions. The study contributes to the development of sustainable materials for environmental remediation, wastewater treatment, and related applications, aligning with ongoing efforts to address water pollution challenges.

Removal of Cr(vi) in wastewater by Fe-Mn oxide loaded sludge biochar.

Sludge biochar loaded with Fe-Mn oxides (FMBC) was prepared and employed to remove Cr(vi) from wastewater. The influences of solution pH, co-existing ion, contact time, adsorption temperature and Cd(vi) concentrations on removing Cr(vi) by FMBC were investigated. The Cr(vi) adsorption on FMBC had strong pH dependence. Additionally, Na+, Mg2+, Ca2+, SiO32-, NO3- and Cl- ions exhibited no influence on Cr(vi) removal efficiency for FMBC, whereas there were inhibition effects of Pb2+, Cu2+, Ni2+, CO32-, SO42-, and PO43- on removing Cr(vi). The Cr(vi) adsorption from solution for FMBC was well described by models of pseudo-second-order and Langmuir, and the largest Cr(vi) removal capacity of FMBC reached 172.3 mg g-1. FMBC had good capacity for treating electroplating wastewater and mineral dissolving wastewater containing Cr(vi). After five regenerations, the 50 and 5 mg L-1 Cr(vi) removing efficiency of FMBC was 82.34% and 97.68%, respectively. The Cr(vi) removal for FMBC involved adsorption-reduction and re-adsorption of Cr(iii) generated by reduction. These results indicated that FMBC has good prospects for remediating Cr(vi)-containing wastewater.

Thermally treated biomass of pine (Pinus kesiya) leaves for effective removal of organic dyes from aqueous solutions

AbstractBACKGROUNDMethyl orange (MO) and methylene blue (MB) from aqueous solutions were effectively removed using thermally treated pine (Pinus kesiya) leaves. The influences of solution pH (2–10), contact time (10–240 min) and initial dye concentration (100–500 mg L−1) were found to be significant in the process of dye removal. The experimental data were fitted with four isotherm models (Langmuir, Freundlich, Sips and Temkin) and four kinetic models (Elovich, pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion). Some mechanisms of the MO and MB adsorption onto the adsorbent material were proposed and discussed.ResultsAmong the four isotherm models examined, the experimental data gave the best fit with the Langmuir model. The maximum Langmuir adsorption capacities were 136.99 mg g−1 for MO and 140.85 mg g−1 for MB. Kinetic studies illustrated that the biosorption of both dyes onto pine leaves aligns with Elovich, pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion models. Thermodynamic studies showed that the uptake of the two dyes was regulated by physisorption, and it was spontaneous and endothermic in nature. Electrostatic interactions, as well as other noncovalent forces such as π–π interactions and hydrogen bonds, were mechanisms of dye adsorption on heat‐treated pine leaf biomass.ConclusionThe present study suggests that pine leaves could be a potential biosorbent for wastewater treatment due to their high availability and production, resulting in several environmental advantages. © 2023 Society of Chemical Industry (SCI).

Follow up of the prostate cancer treatment based on a novel sensing method for anti-prostate cancer drug (flutamide)

In this work, novel modified electrode (MXene/MIL-101(Cr)/GCE) are manufactured through simple layer-by-layer immobilization procedure. The fabricated electrochemical sensor was utilized for electrochemical sensing of flutamide in biological fluids. The immobilization of both MXene and metal-organic framework (MOF) materials on the electrode surface could improve the electrochemical performance of the modified glassy carbon electrode (GCE) towards flutamide due to the synergic effects. The established sensor illustrated the significant sensing ability for the determination of flutamide. The influence of solution pH and volume ratio of MXene/MIL-101(Cr) on electrochemical performance of the modified GCE was researched and optimized. The sensor demonstrated a favorable detection limit of 0.009 μM and a linear range of 0.025–100 μM using differential pulse voltammetry (DPV) technique. The suggested assay illustrated an excellent sensing efficiency towards flutamide in body fluids with recoveries ranging from 97.7% to 102.5%, which indicates its potential in real matrices. In addition, the MXene/MIL-101(Cr)/GCE was illustrated some advantages including simple preparation, good selectivity and reproducibility, and rapid flutamide detection.

Efficient adsorption of bisphenol A by metal-organic frameworks-derived N-doped carbon nanoflakes: Adsorption performance and mechanism investigation

Carbon-based materials have attracted great attentions as one of the most efficient adsorbents for wastewater treatment owing to their outstanding merits of low cost and excellent stability. In this work, we synthesized a novel N-doped carbon nanoflakes (NCF600) with high BET surface area (1609.1 m2/g) via carbonization and etching using UiO-66 as a precursor. Batch experiments demonstrated that NCF600 exhibited a high adsorption capacity for high concentrations of bisphenol A (BPA) in aqueous solutions (200 mg/g for 40 mg/L BPA) within 15 min. Furthermore, NCF600 shown good stability and reusability (the declining efficiency 3.4% after five cycles), following the pseudo-second-order model and the Freundlich adsorption model. Combined with multiple characterizations and density functional theory (DFT) calculations, we observed that pyridinic N is the main adsorption site instead of pyrrolic N and graphitic N. Considering the presence of functional groups in BPA and their interaction with NCF600, along with the influence of solution pH on the adsorption capacity of BPA, it is anticipated that the primary adsorption mechanisms will involve hydrogen bonding and π-π interactions. The present work demonstrates that NCF600 presents broad practical application prospects and provides insights for the design of N-doped carbon-based adsorbents for the effective removal of pollutants.

Influence of solution pH on the properties of biogenic jarosite produced from ferrous ion bio-oxidation in a bioreactor

Precipitation process of ferric ions from bio-oxidation of ferrous ions is influenced by pH and solution chemistry. Accumulation of iron precipitate may reduce extraction efficiency in bioleach operations. Firstly, this study investigates the impact of pH on the properties of iron precipitate generated in a continuous stirred bioreactor at three pH levels (1.7, 1.9, and 2.2). Characterization of precipitates was performed and identified predominantly as potassium jarosite using Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope/energy dispersive spectroscopy (SEM/EDS). Results showed properties of the formed jarosites altered in response to the influent solution pH, with a major effect on the surface area. Secondly, results showed that pseudo-order-kinetic model can accurately describe the sorption performance of the biogenic jarosite with respect to copper uptake. Monomolecular adsorption capacities (qm) at 303 K were 17.12 and 13.32 mg/g for jarosite generated at pH 2.2 and 1.7, respectively. The sorption thermodynamic data showed the process was endothermic and nonspontaneous. Activation energy in this investigation was calculated to be 21.01 and 23.39 kJ/mol for jarosite produced at pH 2.2 and 1.7, respectively, implying that the rate-limiting step is chemically controlled for both adsorption processes. Results of this study may provide some insights into the management of iron precipitation in biohydrometallurgical processes.

Aggregation and disaggregation of Al2O3 nanoparticles: influence of solution pH, humic acid, and electrolyte cations

Aggregation and disaggregation of Al2O3 nanoparticles: influence of solution pH, humic acid, and electrolyte cations

Highly photocatalytic activity of pH-controlled ZnO nanoflakes

ZnO nanoflakes were successfully synthesized by the sol-gel method at a precursor solution pH of 13. The structure, morphology, and photocatalytic activity of the synthesized ZnO nanoflakes were characterized using X-ray diffraction, scanning electron microscope, and ultraviolet–visible spectrophotometer, respectively. The ZnO nanoflakes were highly crystalline semiconductors with an optical band gap of 3.27 eV. The ZnO catalysts revealed a remarkable photocatalytic efficiency toward the degradation of organic dyes including methylene blue (MB), methylene orange (MO), congo red (CR), and rhodamine B (RhB) under UV irradiation. Moreover, the influence of solution pH on photocatalytic activity was also investigated. It was found that the photocatalytic efficiency increased in response to the increase of pH values by degradation of MB, MO, and RhB. However, upon the decrease in pH value, the photocatalytic degradation efficiency of CR was increased. The best result was recorded on the photodegradation of CR with a maximum efficiency of 100% at a pH value of 4 for 10 min.