KOH Modification Research Articles

Eco-friendly remedies for soil contamination: manufacturing and analysis of nanobiochar using sugarcane bagasse and olive mill waste.

Soil degradation poses a significant challenge to Egypt's agriculture, making resource optimization essential. Nanobiochar presents a promising solution for pollutant removal; however, its low yields may hinder commercialization. This study investigates the production of biochar from sugarcane bagasse and olive mill waste, focusing on its composition, morphology, and effectiveness in soil immobilization. Advanced techniques like SEM, TEM, and FTIR were used to characterize the nanobiochar, highlighting its potential as a sustainable solution to soil contamination. The study revealed that ZnCl2 treatment significantly lowers pH, while KOH modification raises it. Surface morphology analysis showed that SCB biochar exhibited a highly porous structure, while OMW biochar had less porous edges and irregular oval-shaped pores. The effects of biochar activation on the availability of heavy metals like Ni, Pb, and Mo (in mg.Kg-1) were also examined. Ni concentrations decreased from 1.27mg.Kg-1 in untreated biochar (NA) to 0.78mg.Kg-1 in KOH-treated biochar (KA) and 0.67mg.Kg-1 in ZnCl2-treated biochar (ZnA). Pb levels dropped from 7.7mg.Kg-1 in NA to 5.2mg.Kg-1 in KA and slightly to 4.74mg.Kg-1 in ZnA. Mo showed a similar trend, with the highest concentration in NA at 1.21mg.Kg-1, followed by 0.88mg.Kg-1 in KA and 0.75mg.Kg-1 in ZnA. Overall, OMW nanobiochar demonstrated a greener, more sustainable solution to soil contamination compared to SCB nanobiochar.

Enhanced Tetracycline Adsorption Using KOH-Modified Biochar Derived from Waste Activated Sludge in Aqueous Solutions.

Antibiotic pollution poses a serious environmental concern worldwide, posing risks to ecosystems and human well-being. Transforming waste activated sludge into adsorbents for antibiotic removal aligns with the concept of utilizing waste to treat waste. However, the adsorption efficiency of these adsorbents is currently limited. This study identified KOH modification as the most effective method for enhancing tetracycline (TC) adsorption by sludge biochar through a comparative analysis of acid, alkali, and oxidant modifications. The adsorption characteristics of TC upon unmodified sludge biochar (BC) as well as KOH-modified sludge biochar (BC-KOH) were investigated in terms of equilibrium, kinetics, and thermodynamics. BC-KOH exhibited higher porosity, greater specific surface area, and increased abundance of oxygen-based functional groups compared to BC. The TC adsorption on BC-KOH conformed the Elovich and Langmuir models, with a maximum adsorption capacity of 243.3 mg/g at 298 K. The adsorption mechanisms included ion exchange, hydrogen bonding, pore filling, and electrostatic adsorption, as well as π-π interactions. Interference with TC adsorption on BC-KOH was observed with HCO3-, PO43-, Ca2+, and Mg2+, whereas Cl-, NO3-, and SO42- ions exhibited minimal impact on the adsorption process. Following three cycles of utilization, there was a slight 5.94% reduction in the equilibrium adsorption capacity, yet the adsorption capacity remained 4.5 times greater than that of unmodified sludge BC, underscoring its significant potential for practical applications. This research provided new insights to the production and application of sludge biochar for treating antibiotic-contaminated wastewater.

Buried interface modification of condensation reflux-processed SnO2 electron transport layers for CsPbBr3 perovskite solar cells

Low temperature solution-processed SnO2 is favorable for electron transport layer (ETL) of flexible perovskite solar cells (PSCs) owing to their process compatibility. Here, we propose a route of condensation reflux-processed SnO2 ETLs for PSCs using SnCl2 source. However, the low temperature SnCl2-derived SnO2 ETLs are inherently associated with a high defect state density as well as a large amount of H+ and Cl- residual on the surface, which will cause open-circuit voltage (VOC) loss of the devices. To tackle this issue, aqueous solutions of KOH, CsOH, and KCl have been employed to regulate the buried interfaces. The effects of different cations (K+ and Cs+) and anions (OH- and Cl-) on the photovoltaic performance of the devices have been comparatively explored. The buried interface with KOH modification showed the best effect, which not only improved the quality and light absorption of CsPbBr3 perovskite layer but also markedly reduced the defect state density at the interface. The optimal device with an architecture of FTO/SnO2/KOH/CsPbBr3/carbon exhibited a champion power conversion efficiency (PCE) of 7.80 %, VOC of 1.46 V, short-circuit current density (JSC) of 7.50 mA/cm2, and fill factor (FF) of 0.71, compared with the pristine counterpart with a PCE of 5.86 %, VOC of 1.40 V, JSC of 6.37 mA/cm2, and FF of 0.66, respectively. The strategy of low temperature-processed SnO2 ETLs by KOH interface modification may also provide an avenue for other-typed flexible PSCs manufacture.

Adsorption and reduction of Cr(VI) by N, S co-doped porous carbon from sewage sludge and low-rank coal: Combining experiments and theoretical calculations

Herein, a novel N, S co-doped porous carbon (S5C5-AC) for Cr(VI) removal was prepared by co-hydrothermal carbonization (HTC) of sewage sludge (SS) and low-rank coal (LC) combining with KOH modification. The results showed that S5C5-AC had excellent adsorption performance on Cr(VI), and lower pH value, higher initial concentration and longer contact time were beneficial for Cr(VI) adsorption. The adsorption kinetics and isotherms revealed that Cr(VI) adsorption by S5C5-AC was homogeneous and dominated by chemisorption. The adsorption isotherm showed that the maximum equilibrium adsorption capacity of S5C5-AC for Cr(VI) was 382.04 mg/g at 25 °C. Furthermore, the results showed that the main mechanisms for Cr(VI) removal were the pore filling, electrostatic interaction and reduction. Moreover, the electron transfer mechanism during the adsorption and reduction process was further explored at the molecular and electronic levels by density functional theory (DFT) and front orbital theory (FOT) simulations. The analysis of DFT and FOT indicated that the synergistic effect between S and N functional groups was exhibited during the Cr(VI) removal process. Considering the existence of synergistic effects between N and S functional groups during adsorption, the S and N content and form were modified collaboratively. Increasing the relative content of pyrrolic N may be the most effective pathway for improving removal performance. Besides that, S5C5-AC exhibited excellent adsorption capacity over a high coexisting ion concentration range and various actual water bodies and regeneration performance, which indicated that S5C5-AC had promising potential for the remediation of wastewater in industrial applications.

Study on removal of oxytetracycline by KOH-modified chestnut shell biochar: Based on two-dimensional spectroscopy and molecular density functional theory

The adsorption type and mode of biochar have been extensive research. However, as an indispensable link to reveal the adsorption mechanism, the study of the adsorption sequence is greatly lacking, especially for different pollutants, the way of adsorption is different. In this study, the observation of the adsorption sequence was amplified by KOH modification and optimization of experimental conditions. Persistent radicals (PFRs) combined with liquid mass spectrometry (LC-MS) eliminated interference from oxidation-reduction. Notability, two-dimensional correlation spectroscopy (2D-COS), Raman and Fourier-transform infrared (FTIR) spectroscopy reveals that the vibration amplitude and velocity of the hydroxyl group are better than those of the carboxyl group, methyl group, and methylene group under time interference. Electrostatic adsorption (EA), H-bood (HB), and π-π* contribute 63.5 %, 35.3 %, and 1.2 %, respectively, to the adsorption of oxytetracycline (OTC). The density functional calculation shows that the nucleophilic and electrophilic reactions of OTC are easy to occur near oxygen atoms and nitrogen atoms. The Fukui function proves that the free radical weight of the N atom is 0.096, which is further confirmed the theoretical predictions by liquid chromatography and four-stage electrostatic field orbital trap mass spectrometry. Finally, this study provides a deeper insight into the biochar adsorption OTC.

KOH-modified hydrochar produced from Cd/Zn hyperaccumulator Sedum Alfredii Hance for aqueous Cd(Ⅱ) removal: Behavior and mechanism

Hydrothermal carbonization (HTC) has been a promising treatment technology of heavy metal-enriched hyperaccumulator biomass to produce superior hydrochar adsorbent for contamination removal from the wastewater. However, a high amount of heavy metal in derived hydrochar limits its further application. In this study, the effect of reaction temperature (180–270 ℃) and medium pH during HTC on heavy metal contents, speciation and leaching risk of hydrochar from the hyperaccumulator biomass Sedum alfredii Hance was investigated to assess its environmental risk. HTC at a low reaction temperature and acid addition facilitated the removal of Zn/Cd/Pb from the solid phase, meanwhile the addition of acid favored the immobilization of Zn/Cd/Pb and lowered the potential leaching risk of Zn/Cd/Pb. Hydrochar prepared from HTC at 240 °C and pH = 2 had lower heavy metal content and lower releasing risk, followed by KOH modification to obtain high adsorption performance. The modified hydrohcar (KSAB) were characterized by SEM, XRD, BET, Boehm titration and FT-IR, and showed that the surface specific surface area and pore structure were optimized and OFGs of hydrochar were improved significantly after KOH treatment. Adsorption experiments showed that the Cd(II) adsorption process onto KSAB well accorded with pseudo-second-order kinetics and Langmuir isotherms. The maximum Cd(II) adsorption capacity of KSAB was 25.69 mg/g, which was 17 times compared to that of pristine hydrochar. Microstructure characteristics and mechanism analysis further suggested that electrostatic interactions, surface complexation, cation-π and ion exchange were the main Cd(II) removal mechanisms of KOH-modified hydrochar. Therefore, hydrochar derived from hyperaccumulator biomass can be used as a highly efficient absorbent to remove Cd(II) from wastewater after KOH modification.

Synthesis of corncob biochar with high surface area by KOH activation for VOC adsorption: effect of KOH addition method

AbstractBACKGROUNDCarbon materials have been regarded as valuable adsorbents for removal of volatile organic compounds (VOCs) owing to their high specific surface area and abundant pore structure. However, the complexity and high cost of the process used to treat the feedstock to produce commercial activated carbon has limited its application. In this reported study, a series of biochar materials was prepared using the KOH modification method employing corn cob as the raw material. The effects of different potassium hydroxide dosages, various activation temperatures and the activator addition method on the structure, physicochemical properties and VOC adsorption performance of the resulting biochars and their structure–activity relationship were systematically studied.RESULTSAdsorption performance tests and a series of characterization results showed that the CC‐3‐700 (corn cob/KOH = 1:3, T = 700 °C, two‐step dry mixing pyrolysis method) sample had highest toluene dynamic adsorption capacity (up to 573.5 mg g−1) compared to the other prepared samples. This result was attributed to the maximum specific surface area (2349 m2 g−1) and pore volume (1.22 cm3 g−1) of this sample. Moreover, the result suggested that the high specific surface area, abundant pore structure and highly disordered non‐graphitizable carbon in sample CC‐3‐700 were the major reasons for its excellent adsorption performance. The results of a multi‐component adsorption performance test showed that corn cob biochar had a strong adsorption capacity for toluene when simultaneously exposed to benzene and toluene.CONCLUSIONThe results of this study revealed that the corn cob biochar prepared using a two‐step roasting method offers good potential prospects for application in the field of VOC pollution control. © 2023 Society of Chemical Industry (SCI).

A Comprehensive Study on the Interactive Effects of Carbon Crystallinity and Electrochemical Activation for KOH-Modified Soft Carbons and Their High-Voltage Supercapacitor Application

The interactive influences between carbon crystallinity and electrochemical activation (EA) on the capacitive behavior for a series of soft carbons (SCs) modified with KOH have been systematically examined for the high-voltage (≥ 4.0 V) super-capacitors in the conventional liquid electrolyte of 1 M tetraethylammonium tetra-fluoroborate/propylene carbonate (TEABF4/PC). The energy storage behavior of SCs without and with the KOH modification as well as before and after the EA treatment in various potential regions are investigated by galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) tests. Characterizations including scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption/desorption isotherms are employed to probe possible changes in carbon structure after the KOH and EA treatments. The results show that the specific capacitance of SCs can be significantly promoted by the KOH modification through crystallinity reducing and the EA via the irreversible insertion of either BF4 − or TEA+. The EA process is found to be more effective for KOH-modified SCs with relatively low crystallinity. After the optimization of both positive and negative electrodes, a 4 V full cell with the specific energy of 71.2 and 54.9 Wh kg−1 at the specific power of 0.9 and 6.1 kW kg−1 can be obtained. This 4 V supercapacitor also delivers the superior energy density of 37.7 Wh l−1 at 0.5 kW l−1 and 29.1 Wh l−1 at 3.2 kW l−1. For the stability, the 4 V supercapacitor exhibits about 85% capacitance retention after 10000 GCD cycles. The results have demonstrated the application potential of KOH-modified SCs as promising electrode materials for the high-voltage supercapacitors.

Removal of cobalt ions (II) from simulated radioactive effluent by electrosorption on potassium hydroxide modified activated carbon fiber felt

In this study, the electrosorption property of potassium hydroxide modified activated carbon fiber felt (ACFF-KOH) to Co2+ in simulated radioactive effluent was evaluated. Factors influencing the electrosorption such as applied voltage, initial concentration, pH, cyclic flow rate, competitive ions and cycle numbers on Co2+ removal rate were investigated. Kinetic models and isotherm models were used to evaluate the electrosorption performance of ACFF-KOH. The results showed that the voltage enhanced the removal capacity of Co2+, which raised from 5.92 to 14.80 mg·g−1 when the applied voltage increased from 0 to 1.6 V. Higher initial concentration of the solution induced larger electrosorption capacity. In addition, the optimal adsorption pH of the electrosorption was around 5. When competing ions exist, the removal rate of Co2+ decreased. Furthermore, ACFF-KOH had excellent cycling performance, and the removal rate remained above 85 % after 6 cycles. The pseudo-first-order (PFO) model fitted the data better than the pseudo-second-order (PSO) model, indicating that physisorption was the rate-limiting step during the eletrosorption process. As the Langmuir isotherm had a higher regression coefficient (0.9983) than the Freundlich isotherm, monolayer adsorption was the main adsorption mechanism for Co2+ on the ACFF-KOH electrode. The BET results showed that KOH modification improved the pore parameters of ACFF. According to the XPS and XRD results, Co(OH)2 precipitates were generated on the electrode surface after electrosorption. The above results indicated that ACFF-KOH had excellent electrosorption and regeneration performance for Co2+ in aqueous solution, thus it has great application value in the treatment of cobalt-containing radioactive effluent.

A study on and adsorption mechanism of ammonium nitrogen by modified corn straw biochar.

Using corn stover as raw material, the adsorption mechanism of ammonium nitrogen by biochar prepared by different modification methods was studied. The biochar was characterized by Fourier transform infrared spectroscopy, surface-area analysis and scanning electron microscopy. The results showed that the adsorption of by different modified biochars confirmed the quasi-second-order kinetic equation (R 2 > 0.95, p ≤ 0.05), the adsorption isotherms of the Langmuir equation (R 2 ≥ 0.96, p ≤ 0.05). ΔG θ < 0, ΔH θ > 0 indicated that the adsorption of by different modified biochars was a spontaneous endothermic reaction. With the increase in adsorption temperature, the adsorption capacity of biochar to ammonium nitrogen increased gradually. The adsorption was monolayer adsorption and was controlled by a fast reaction. Both KOH and FeCl3 modified biochars significantly improved the adsorption capacity of , and the adsorption mechanism was different. The adsorption capacity of by FeCl3 modified biochars mainly increased the specific surface area and micropore volume. The adsorption of ammonium nitrogen after KOH modification primarily depended on the wealthy oxygen-containing functional groups. The adsorption effect of ammonium nitrogen modified by KOH was better than that of biochar modified by FeCl3.

Characterization and properties of hydroxyapatite with KOH modification for lead (II) removal

Characterization and properties of hydroxyapatite with KOH modification for lead (II) removal

KOH modification of fluorinated graphite and its reaction mechanism

KOH electrochemical method and heating method were employed to modify fluorinated graphite and explore the modification mechanism. The chemical composition and microstructure of the products were characterized and analyzed before and after the reaction. As the electrochemical reaction time or heating temperature increased, the carbon fluorine bond gradually underwent a nucleophilic reaction with KOH according to its reactivity, promoting the formation of fluorine ions in the residual product and carbon oxygen bonds in the corresponding oxidized fluorinated graphite (OFG). The electrochemical method with the anode on the bottom and the heating method were insufficient to allow the isolated carbon fluorine bond to react, retaining some carbon fluorine bonds. By positioning the anode on top, electron transfer significantly accelerates the activation of the carbon fluorine bond, which then reacts completely. According to theoretical simulation calculations, electronegative groups around the carbon fluorine bond can effectively enhance its reactivity.

Insights into CO2 adsorption on KOH-activated biochars derived from the mixed sewage sludge and pine sawdust

The environment issues associated with global warming and climate change caused by continuous increase in greenhouse gas emissions have attracted worldwide concerns. As renewable resources with good adsorption property, biochar is an efficient and environmental friendly adsorbsent for CO2 capture. In this study, the CO2 adsorption behavior of biochars derived from feedstock mixtures of 70% pine sawdust and 30% sewage sludge by KOH modification was investigated. The textual properties and functional groups of the pristine biochars have been significantly enhanced after KOH activation. With highly developed microporosity, the specific surface area (SSA) of the KOH-modified biochars increased by 3.9–14.5 times. Furthermore, higher CO2 adsorption capacities of 136.7–182.0 mg/g were observed for the modified biochars, compared to pristine ones (35.5–42.9 mg/g). The development of micropores by KOH activation significantly increased the CO2 adsorption capacity. Meanwhile, the presence of hetero atoms (O and K) also positively influenced CO2 adsorption capacity of biochar. Noticeably, both physical and chemical adsorption played a crucial role in CO2 capture, which was verified by different characterization methods including high resolution scanning electron microscope, X-ray photoelectron spectroscopy and in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The Findings of this study demonstrate the -significance of chemical sorption by identifying the transformation of CO2 by biochar composites and in situ characterization of weakly adsorbed and newly formed mineral species during the CO2 sorption process. Moreover, BC700K showed 97% recyclability during 10 consecutive adsorption-desorption cycles at 25 °C, 1 bar. The results obtained in the present study may inspire new research interest and provide a comprehensive insight into the research subject to biochars derived from feedstock mixtures for CO2 capture.

Biochars derived from by-products of microalgae pyrolysis for sorption of gaseous H2S

KOH-modified biochars derived from by-products of microalgae pyrolysis were prepared to adsorb gaseous H2S. Influences of various parameters (e.g., mass ratio between KOH and biochars, and adsorption temperature) on desulfurization performance were investigated. Kinetics/mechanisms of H2S adsorption, and reutilization of spent adsorbents for capturing gaseous Hg0 were also explored. Results exhibited that KOH modification greatly improved the desulfurization performance of biochars via improving the pore structures of biochar and increasing the surfaces oxygen-containing group. The modified biochars (CK2 and SK2) achieve optimal desulfurization performance, with an adsorption capacity of 59.10 mg/g for CK2 and 42.30 mg/g for SK2, respectively. Adsorption temperature showed a double effect on desulfurization. S0 and sulfate were successfully detected on biochar surface after adsorption via XPS and XRD analysis, indicating that chemical adsorption occurred in the H2S adsorption. Kinetic study showed that physical adsorption governed the H2S adsorption process, and mass transfer was the main control step of the desulfurization process. The spent adsorbents (i.e., spent containing-sulfur biochars) could capture efficiently Hg0 in gas and shown good competitiveness as compared with commercial activated carbon.

KOH modification effectively enhances the Cd and Pb adsorption performance of N-enriched biochar derived from waste chicken feathers.

Waste chicken feathers are the ideal precursor for the production of low-cost N-enriched biochar. KOH-modified N-enriched biochar (KNB) containing 15.92wt% N was successfully prepared using waste chicken feathers. The adsorption kinetics results showed that KNB had rapid Cd (2h) and Pb (1h) adsorption rates. The Cd and Pb adsorption capacities of KNB (the values of KF were 22.324 (Cd) and 119.654 (Pb) mg1-(1/n)·L1/n·g-1) were 7.07 and 26.52 times higher than those of the original biochar based on the adsorption isotherm results. The KNB was stable at pH 3-6 and had stronger co-adsorption capacities in double-ion systems. Based on the adsorption experiments and various characterization methods, we concluded that the primary Cd and Pb adsorption mechanisms of KNB involved electrostatic interactions, cation-π interactions, complexation, and K+ exchange. The precipitation mechanism could partially account for Pb adsorption but not for Cd adsorption. KOH modification enhanced the electronegativity of biochar and then increased the electrostatic attraction. Surface O- and N-containing functional groups were involved in Cd and Pb adsorption. Graphitic-N, oxidised-N, and OCO were the main active adsorption groups, the relative contents of which increased after KOH modification, thus increasing the Cd and Pb adsorption performance. Therefore, KNB can be used as a fast and highly efficient adsorption agent to remove Cd and Pb from wastewater containing either Cd and Pb or a combination of these two metals.

Porous Biochars Derived from Microalgae Pyrolysis for CO2 Adsorption

In order to slow down the greenhouse warming caused by excessive CO₂ emissions and effectively exploit the byproducts produced during the biofuel production process, N-doped porous biochars derived from the byproducts of microalgae (chlorella and spirulina) pyrolysis by combining urea and KOH modification were synthesized in this article to remove CO₂ in simulated flue gas. The physicochemical properties of the microalgae porous biochars were investigated via characterization tools, involving pH, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). CO₂ adsorption kinetics, thermodynamics, and CO₂ adsorption performance were also studied. Results reveal that the functional groups and specific surface areas of microalgae biochars are substantially increased via urea and KOH modification, and nitrogen-containing functional groups (mainly involving N–H, C–N, etc.) are major adsorption sites for CO₂ adsorption. The key control step for CO₂ adsorption is external mass transfer, and the CO₂ adsorption process over the microalgae porous biochars is mainly physical adsorption. Moreover, the chlorella-based porous biochars CNK-2 and spirulina-based porous biochars SNK-2 have optimal CO₂ removal performances, and their maximum adsorption capacities, respectively, reach 3.44 and 3.09 mmol/g at 25 °C. The results of regeneration studies demonstrate that, after 10 regeneration experiments, CNK-2 and SNK-2 still possess high CO₂ sorption performances (reaching 3.09 and 2.78 mmol/g, respectively), exhibiting good regeneration potential.

Understanding the synergy between N-doped ultra-microporous carbonaceous adsorbent and nitrogen functionalities for high performance of CO2 sorption

Porous carbonaceous adsorbents are believed to encourage contenders to CO2 uptake however their high production cost has urged researchers towards cheap renewable. In this study, nitrogen-doped carbonaceous adsorbents with high ultra-microporous structure were synthesized by carbonization and activation of chitosan along with urea and KOH simultaneously at various temperatures (600−900 °C). The effects of temperature, urea modification, and chemical activation on nitrogen functionalities and development of porous structure were analyzed. Results showed that porous carbons synthesized with urea and KOH modification at 700 °C exhibit the highest CO2 adsorption value (5.92 mmol g−1 at 0 °C and 4.45 mmol g−1 at 25 °C). Enhanced adsorption by NCABC-700 was found due to synergistic effect of nitrogen as well as high specific surface area (1404 m2 g−1) and micropore volume (0.68 cm3 g−1), respectively. Furthermore, best fitting of Freundlich isotherm model explained heterogeneous nature of adsorbent. Isosteric heat of adsorption with a value of 42.2 kJ mol-1, also indicated the presence of N containing functional groups and a high number of micropores that created a strong interaction between adsorbent and adsorbate, helping in high CO2 uptake.

Comparative analysis of linear and nonlinear equilibrium models for the removal of metronidazole by tea waste activated carbon.

Tea waste was carbonized at 400 °C for 45 min and modified with potassium hydroxide (KOH), to enhance the active sites for the adsorption of antibiotics. The developed tea waste activated carbon (TWAC) was used as a novel eco-friendly and cost-effective adsorbent for metronidazole (MZN) removal from aqueous solution. The textural and surface properties of the adsorbent were determined using Brunauer-Emmett-Teller (BET) and FT-Raman analysis. The BET surface was found to have increased from 24.670 to 349.585 after carbonization and KOH modification. The batch experimental parameters were optimized and equilibrium time was found to be 75 min. Linear and non-linear models were carried out on the adsorption isotherm and kinetics to determine the best fit for the adsorption data. The adsorption equilibrium data were well fitted by the Freundlich isotherm and pseudo-second order models, with higher regression correlation (R2) and smaller chi-square (χ2), as predicted by the non-linear model. The thermodynamic results revealed the adsorption of MZN as spontaneous, physical, and consistently exothermic in character. The activation energy value of 7.610 kJ/mol further revealed that the adsorption process is dominated majorly by physical adsorption. The removal of MZN onto TWAC was best described by the non-linear adsorption isotherm and kinetics model.

Fabrication and Properties of Polyimide/Aluminum Oxide Composite Films via Different Alkali Etching and Ion Exchange Technique

The polyimide (PI)/aluminum oxide (Al2O3) composite films were prepared via alkali surface modification and ion exchange technique on flexible PI films. Firstly, the polyamide acid layers were formed on both surfaces of PI film through chemical surface modification in aqueous KOH and NaOH solution, respectively. Subsequently the ion exchange process was processed in AlCl3 aqueous solution. After final thermal annealing in air, the aluminum ions which exchanged on both surfaces of PI film became continuous Al2O3 composite layers. The surface morphology, microstructures, thermal and electrical properties of the PI/Al2O3 composite films were tested by the scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), electric breakdown voltage and corona-resistant measurement. Results from SEM measuring revealed that the surfaces of composite films became much rougher with the increasing alkali treatment time. FT-IR spectrums showed that the treatments of alkali surface modification and ion exchange had no effect on molecular structure of polyimide. TGA results showed that the excellent thermal properties of the film are maintained. Electric breakdown voltage of composite films showed monotonically decreased with the increasing alkali treatment time. Corona-resistant test results showed that the best corona-resistant times of composite films which using NaOH and KOH modification were up to 22.6 minutes and 15.4 minutes, respectively.

Formation of a Ni(OH)2/NiOOH active redox couple on nickel nanowires for formaldehyde detection in alkaline media

Highly ordered, Ni(OH)2Ni-nanowire-based receptor elements were electrochemically fabricated and tested for formaldehyde (HCHO) detection by monitoring their oxidation ability in alkaline media. In order to normalize the electrochemical output currents, the Ni nanowires' electrochemically active surface area was assessed using an oxalate-based method after the template was released. The electrochemical transformation of the Ni-nanowire surfaces to a Ni(OH)2/NiOOH redox couple was performed in 0.5-mol L−1 KOH using cyclic voltammetry at 200 mV s−1. The transformation was monitored for two cases: without KOH modification and with KOH-modified Ni nanowires. It was shown that the non-modified Ni nanowires possess a poor electrochemical response to HCHO oxidation, mainly due to the formation of a NiO surface layer. On the other hand, the modified Ni nanowires donated an electron to the HCHO oxidation reaction, resulting in high output-current densities, attributed to the thin Ni(OH)2/NiOOH layer, its amorphous state (TEM/SAED) and its small work function, due to electron doping from under the layered Ni. The modified Ni-nanowire-based electrodes had high sensitivity, reproducibility, selectivity and a low detection limit (0.8 μmol L−1). The developed HCHO Ni-nanowire-based electrodes’ characteristics surpass other Ni-based nanostructured electrodes and have limits of detection comparable to those achieved with noble metals.