Catalytic Ozonation Of Oxalic Acid Research Articles

Metal-free N-doped spongy carbon recycled from waste MOF for enhanced catalytic ozonation: Mechanistic insights and practical applications

At present, considerable efforts have been devoted to the development and application of MOFs, and some MOFs have realized industrial mass production and sales. However, little attention was paid to the treatment and disposal of the resulting waste MOF. In this study, the antibiotic(N source)-saturated waste MOF adsorbent was recycled into metal-free N-doped carbocatalyst through one-step pyrolysis. Compared with the pristine MOF-derived undoped carbon, N-doping led to nearly 2-fold enhancement in the pseudo-first-order rate constant for catalytic ozonation of oxalic acid (OA), and the COD removal of coking and swine wastewaters reached more than 60 % within 30 min. Apart from the formation of spongy porous morphology and the boosting of specific surface area from 253.7 to 320.6 m2/g after N doping, the characterization analysis and OA degradation results revealed that oxygen vacancies, hydroxyl groups and N species were the main active sites. Furthermore, it was identified the dominant contribution of OH in OA destruction, followed by O2— and 1O2, and the metal-free N-doped carbon displayed good reusability and chemical stability. This study proposes a feasible strategy for the utilization of waste MOF, showing great reference significance for the expansion of material functions.

Catalytic Ozonation of Oxalic Acid in Aqueous Solution in the Presence of Manganese Ions

Catalytic Ozonation of Oxalic Acid in Aqueous Solution in the Presence of Manganese Ions

A magnetic-void-porous MnFe2O4/carbon microspheres nano-catalyst for catalytic ozonation: Preparation, performance and mechanism

Wastewater treatment is essential to guarantee human health and ecological security. Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology. However, this method has always been limited by nanocatalysts disadvantages such as easily loss, difficult to separate and reuse, and catalytic ability decay caused by aggregation, which could cause severe resources waste and potential risk to human health and ecosystem. To remedy these challenges, a magnetic-void-porous MnFe2O4/carbon microsphere shell nanocatalyst (CMS-MnFe2O4) was successfully synthesized using renewable natural microalgae. The separation test showed CMS-MnFe2O4 was rapidly separated within 2 min under an external magnetic field. In catalytic ozonation of oxalic acid (OA), CMS-MnFe2O4 showed efficient and stable catalytic efficiency, reaching a maximum total organic carbon removal efficiency of 96.59 % and maintained a 93.88 % efficiency after 4 cycles. The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell, which significantly enhanced CMS-MnFe2O4 chemical stability and reduced the metal ions leaching to 10–20 % of MnFe2O4 through electron transfer. To explore the catalytic mechanism, radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed. Consequently, this study suggests that an efficient, recyclable, stable, and durable catalyst for catalytic ozonation could be prepared.

Heterogeneous catalytic ozonation of oxalic acid with an effective catalyst based on copper oxide modified g-C3N4

Various amounts of copper oxide (CuO) modified graphitic carbon nitride (g-C3N4) denoted as CuO-CNx composites were successfully fabricated via a reflux condensation method and used as efficient ozonation catalysts for oxalic acid (OA) degradation in aqueous solution. The BET, FT-IR, HRSEM, TEM, XPS, etc. characterizations revealed the chemical composition, bond structure and morphologies of as-prepared CuO-CNx composites. The results indicated that the introduction of CuO into g-C3N4 relying on the chemical interaction rather than simple physical mixture. Moreover, the increased active sites and the intense chemical bonds could play important roles in improving the catalytic ozonation performances of CuO-CNx composites. In this study, the practical applications of catalysts at different conditions were also investigated. When the mass ratio of CuO/g-C3N4 was 10, the CuO-CN10 composite exhibited superior catalytic ozonation activity with 97.9% OA removal efficiency after 30 min at pH 5.0. Meanwhile, the CuO-CN10 showed excellent stability and reusability for contaminant degradation during multiple consecutive cycles. Furthermore, hydroxyl radical and superoxide radical as the major reactive radicals were identified and the catalytic mechanism for OA degradation improvement was also elucidated. Overall, this work would provide an efficient and eco-friendly catalyst for water treatment as well as a new idea for future environmental purification.

Occurrence of both hydroxyl radical and surface oxidation pathways in N-doped layered nanocarbons for aqueous catalytic ozonation

Metal-free catalysts such as N-doped nanocarbons are sustainable alternatives to metal-based catalysts for the degradation of persistent organic pollutants (POPs), but cost-efficient methods are required for their large-scale synthesis. In this study, a facile and scalable strategy was established for synthesizing layered N-doped nanocarbons via the pyrolysis of β-cyclodextrin (β-CD) and melamine in a N2 atmosphere. Compared with undoped pyrolyzed β-CD, N-doping led to a 30.3-fold enhancement in the pseudo-first-order rate constant for catalytic ozonation of oxalic acid (OA), and complete degradation of 50 mg/L OA was achieved in 45 min. Apart from the specific surface area boosting from 78.9 to 16.2 m2/g after N doping, the OA degradation results and material characterization also suggested that quaternary N was the main active site, which was further validated by density functional theory (DFT) simulations. DFT simulations also suggested that C atoms with high charge densities adjacent to N dopants exhibited considerable potential for the catalytic dissociation of ozone. Electron paramagnetic resonance (EPR), radical quenching, and in situ Raman studies indicated occurrence of surface oxidation pathway apart from the radical-based one. Ozone on the catalyst surface was decomposed into surface-adsorbed atomic oxygen (*Oad) and free peroxide (*O2 free). Both *Oad and OH, which was further evolved on the surface or in bulk solution, contributed to OA destruction. These insights into the catalytic ozonation mechanism on N-doped nanocarbons will advance their practical application to the catalytic degradation of organic pollutants.

An Optimization Study of Cobalt Supported on Activated Carbon for the Catalytic Ozonation of Oxalic Acid: Effect of Operating Parameters and Synergetic Combination

ABSTRACTIn this study, new heterogeneous cobalt (Co) catalysts supported on activated carbon (Co/AC) were developed using a wetness impregnation process. The effect of preparation conditions on catalyst characteristics was examined. This work focused on two key parameters: the impregnation rate and the calcination atmosphere (temperature and time). Different catalysts were prepared by varying the Co loading on AC. Various catalysts were characterized by means of nitrogen sorptiometry at 77K, Boehm and pHpzc analysis. It was found that the catalyst properties and the functional surface groups were affected by the operating conditions. The best surface area was 997.5 m2/g obtained when the activated carbon was impregnated with 5% Co loading and calcined at 350°C for 2 h. The effects of parameters, such as cobalt loading, pH, catalyst dose, and ozone dose, were explored on oxalic acid removal (OA). Results show that the use of Co/AC for heterogeneous catalytic ozonation enhanced the degradation efficiency of oxalic acid (OA) significantly compared with simple ozonation and O3/AC. The main results indicate that the optimum catalytic activity was observed when 5% (wt/wt) of Co was supported on AC reaching a catalytic ozonation efficiency of 95%. The results of total organic carbon removal of 91% were achieved at optimum conditions.

Catalytic Ozonation of Oxalic Acid in the Presence of Fe2O3-Loaded Activated Carbon

ABSTRACTThe activity and optimum condition of metal-loaded activated carbon catalyst (Me/AC) for oxalic acid (OA) ozonation were evaluated. Results showed that Fe-loaded activated carbon (Fe/AC) showed better activity in five kinds of Me/AC catalysts prepared by a dipping method. Fe catalyst, crystallizing as γ-Fe2O3, dispersed well on AC surface. Fe2O3/AC, with 1.12% Fe weight ratio and 450°C calcination temperature and showed better activity for OA ozonation. 89.2% of OA was removed in the Fe2O3/AC/O3 process, which was higher than those in AC/O3 (79.6%) and O3 (3.2%) processes. The calcination process helped to promote adsorption capability and catalytic activity of AC. In addition, Surface hydroxyl groups played a key role in Fe2O3/AC’s catalytic activity. Acidic condition was more favorable for OA removal in the Fe2O3/AC/O3 process. A hydroxyl radical (•OH) oxidation mechanism was proven in Fe2O3/AC/O3. The catalytic activity of Fe2O3/AC remained satisfactory after several cycles, indicating that Fe2O3/AC had a good reusability property.

Catalytic ozonation of oxalic acid over rod-like ceria coated on activated carbon

A catalyst consisting of rod-like ceria coated on activated carbon (CeO2@AC) was prepared by an urea-mediated hydrothermal procedure and used towards ozonation of oxalic acid (OA) in water. The results showed that CeO2@AC exhibits good catalytic activity with excellent stability. The ozonation reaction catalyzed by CeO2@AC led to a complete removal of OA (1.5 mM, 0.5 g/L catalyst) in 60 min and showed a 75% increase in OA removal compared to the single non-catalytic ozonation. After five consecutive reuse cycles, CeO2@AC showed almost the same catalytic performance with few only changes in ceria content and surface morphology.

Activity assessment of direct synthesized Fe-SBA-15 for catalytic ozonation of oxalic acid

Abstract Highly ordered Iron-doped SBA-15 mesoporous material (Fe-SBA-15), which was synthesized via a direct hydrothermal method under weak acid condition, was used as heterogeneous catalyst for the ozonation of oxalic acid in aqueous solution. The results indicated that Fe doping significantly improved the catalytic activity of SBA-15, a high oxalic acid removal of 86.6% was achieved under the chosen condition, only 30.2% for SBA-15/O3 process. The major operating variables including Si/Fe ratio in catalyst, initial pH value and radical scavenger were also studied for catalytic reaction mechanism. The active sites of Fe-SBA-15 increased with iron doping content and Fe-SBA-15 significantly influenced ozone concentration in aqueous solution. The catalytic efficiency was mainly affected by radical scavenger and the pH value of solution, which illustrated that the catalytic ozonation process followed free radical mechanism, and the surface reaction played a critical role for oxalic acid degradation. The stability of Fe-SBA-15 was verified by the reused experiments. The XRD and BET tests also demonstrated that Fe-SBA-15 retained highly ordered 2D-hexagonal mesoporous structure and large surface area after reused. Fe-SBA-15 was a promising catalyst for catalytic ozonation of oxalic acid.

Intrinsic Activity of SBA-like Silica in the Catalytic Ozonation of Organic Pollutants

ABSTRACTHydrothermal synthesis using two gel compositions: i. 1 SiO2: 0.059 P123: 56.130 HCl: 607.638 H2O; ii. 1 SiO2: 0.006 P123: 0.013 F127: 42.439 HCl: 442.876 H2O, resulted in highly crystalline SBA-15 and SBA-16 like silica with intrinsic activity in the catalytic ozonation of oxalic acid (OA), phenol (φ-OH) and Orange G (OG) in water at room temperature. X-ray diffraction, nitrogen adsorption–desorption, transmission and scanning electron microscopies revealed highly ordered mesoporous structure, with large surface area, regular channels and uniform particle size. UV-Vis analysis provided faster, more precise and reliable assessments of the decomposition yield and process selectivity than the conventional and laborious method of Chemical Oxygen Demand (COD). The ozone reactivity was found to be favored by increasing size of the organic substrate. OG and phenol decomposition required shorter ozonation time (20, 15 min, respectively) than OA, involving mainly phenyl ring hydroxylation and cleavage. Measurements through thermal programmed desorption of carbon dioxide and water revealed that the catalytic activity of the SBA samples involves adsorption via both acid-base and hydrophobic interactions. Suitable SBA modifications allow tailoring these interactions for even faster ozonation without persistent traces of short chain derivatives.

Carbonized polyacrylonitrile fibers for the catalytic ozonation of oxalic acid

Textile polyacrylonitrile (PAN) fibers, which contain nitrogen, were carbonized at different temperatures and activated during 10h in order to assess their performance as ozonation catalysts in the oxalic acid degradation The fiber carbonized at 800°C shows the best performance due to its basic character and, mainly, the high concentration of nitrogen surface groups, particularly N-pyridinic (N6) groups. The carbonization of PAN fibers is a simple and effective method to prepare materials with good catalytic activity in ozonation processes

Catalytic ozonation of organic compounds in water over the catalyst of RuO2/ZrO2-CeO2

This research investigates the performances of RuO2/ZrO2-CeO2 in catalytic ozonation for water treatment. The results show that RuO2/ZrO2-CeO2 was active for the catalytic ozonation of oxalic acid and possessed higher stability than RuO2/Al2O3 and Ru/AC. In the catalytic ozonation of dimethyl phthalate (DMP), RuO2/ZrO2-CeO2 did not enhance the DMP degradation rate but significantly improved the total organic carbon (TOC) removal rate. The TOC removal in catalytic ozonation was 56% more than that in noncatalytic ozonation. However this does not mean the catalyst was very active because the contribution of catalysis to the overall TOC removal was only 30%. The adsorption of the intermediates on RuO2/ZrO2-CeO2 played an important role on the overall TOC removal while the adsorption of DMP on it was negligible. This adsorption difference was due to their different ozonation rates. In the catalytic ozonation of disinfection byproduct precursors with RuO2/ZrO2-CeO2, the reductions of the haloacetic acid and trihalomethane formation potentials (HAAFPs and THMFPs) for the natural water samples were 38%–57% and 50%–64%, respectively. The catalyst significantly promoted the reduction of HAAFPs but insignificantly improved the reduction of THMFPs as ozone reacts fast with the THMs precursors. These results illustrate the good promise of RuO2/ZrO2-CeO2 in catalytic ozonation for water treatment.

Influence of the surface hydroxyl groups of MnOx/SBA-15 on heterogeneous catalytic ozonation of oxalic acid

Comparative ozonation experiments were carried out to investigate the catalytic ability and mechanism of SBA-15 supported manganese oxide (MnOx/SBA-15) for the degradation of oxalic acid (OA) in aqueous solution. The results showed that MnOx/SBA-15 possessed good catalytic capacity for the ozonation of OA. The influences of tert-butanol and phosphate on OA removal and ozone equilibrium concentration in aqueous solution demonstrated that initiation of hydroxyl radicals (OH) was involved and surface reaction played the major role in O3/MnOx/SBA-15. The effects of manganese content and initial solution pH verified that surface hydroxyl groups affected by the pH of solution and the point of zero charge (pHPZC) of catalysts, were closely related to OA adsorption and OH initiation on the surface of MnOx/SBA-15. The pre-ozonated catalyst improved its catalytic activity a little due to the enhancement of electron transfer in the presence of higher multivalent MnOx (Mn(III)/Mn(IV)). It was concluded that the protonated surface hydroxyl groups were the main reaction sites and a possible catalytic ozonation mechanism of OA over MnOx/SBA-15 was proposed.

Promoting effect of nitration modification on activated carbon in the catalytic ozonation of oxalic acid

A commercial activated carbon (AC) was modified with a nitration or amination method, and the effects of textural and chemical properties on the ability of the AC samples to destroy oxalic acid (OA) using ozone was investigated in this work. The degradation rates of OA on the nitrated and aminated AC samples increased by 38.5% and 9.6%, respectively. The adsorption capacity of the AC sample was not enhanced after modification, but the decomposition rate of ozone in solution increased. The surface area of AC significantly decreased after nitration because the entrance of micropores and some larger pores were blocked by the modified functional groups. In addition, the surface area was recovered when the nitrated AC was further aminated. We demonstrated that the enhancement in the catalytic activity was primarily caused by the differences in surface chemistry. The pHpzc values and Boehm titration results showed that nitration increased the acidity of the AC, while more basic groups were grafted after amination. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) results confirmed that–NO2 and acid oxygenated groups were simultaneously grafted onto AC during nitration. Meanwhile, the –NO2 group was completely reduced to NH2 and the carboxylic groups were partially reduced during amination. The basic groups (NH2 and possible pyrone groups) enhanced the catalytic activity of the aminated AC sample, and the increased activity of the nitrated AC material was mainly due to the acid oxygenated surface groups.

Lanthanum-based perovskites as catalysts for the ozonation of selected organic compounds

The ozonation of two model compounds (oxalic acid and dye C. I. Reactive Blue 5) was carried out in the presence of La containing perovskites prepared by the citrate method. With the exception of LaFe0.9Cu0.1O3, all samples are active in the catalytic ozonation of oxalic acid, some of them allowing fast degradation of the compound. The presence of lattice vacancies on the perovskites surface and tuning of oxidation ability by the B cation play a key role in oxalic acid removal. Sample LaCoO3 was considered the best catalyst in oxalic acid degradation; in addition to its high activity, no metal leaching was observed. Regarding colour removal from the dye solution, single ozonation was slightly more efficient than catalytic ozonation in the presence of LaCoO3. On the other hand, ozonation catalyzed by LaCoO3 improved the TOC removal, allowing almost complete mineralization of the solution after 3h of reaction under the conditions tested.

Catalytic ozonation of oxalic acid using carbon nanofibres on macrostructured supports

Carbon nanofibres (CNFs) were grown on different macrostructured supports such as cordierite monoliths, carbon felts and sintered metal fibres. The resulting composites exhibited excellent resistance to attrition/corrosion and its porosity is mainly due to mesoporous structures. The CNF/structured materials were tested in the ozonation of oxalic acid in a conventional semi-batch reactor after being crushed to powder form, and in a newly designed reactor that may operate in semi-batch or continuous operation. The CNFs supported on the different structured materials exhibited high catalytic activity in the mineralization of oxalic acid.

Catalytic Ozonation of Oxalic Acid Using SrTiO3 Catalyst

A new catalyst, strontium titanate (SrTiO3), has been successfully employed to degrade oxalic acid in catalytic ozonation process. About 4.5%, 9.3% and 45.8% of oxalic acid removal efficiencies were noted in adsorption, ozonation, and catalytic ozonation processes, respectively, which demonstrates the catalytic activity of SrTiO3 towards ozone. The optimum amount of catalyst loading on decomposing oxalic acid was found to be 1.25 g/L. The catalytic stability was investigated up to four successive cycles and found that the catalyst was still stable and efficient.

FeOOH catalytic ozonation of oxalic acid and the effect of phosphate binding on its catalytic activity

The catalytic activity of FeOOH on ozonation of oxalic acid at pH 4.0 and 7.0 conditions was investigated in a semi-continuous experimental mode. The results indicate that FeOOH can effectively promote the generation of hydroxyl radicals (OH) under acidic and neutral pH conditions, resulting in the enhancement of the degradation efficiency of oxalic acid by ozone. It is deduced that the hydroxyl groups both of in neutral state (Me-OH) and positive charge state (Me-OH2+) can perform as the active sites for ozone decomposition into hydroxyl radicals generation. The ligand exchange of hydroxyl groups by phosphate adsorption deteriorates the catalytic activity of FeOOH on ozonation, but the phosphate is found to desorb from FeOOH during the catalytic ozonation process, resulting in the reactivation of the catalytic activity of FeOOH.

Effect of ozonation pretreatment on the surface properties and catalytic activity of multi-walled carbon nanotube

Multi-walled carbon nanotube (MWCNT) has been used in the catalytic ozonation of oxalic acid in aqueous solution, which was pretreated using ozone and was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption and Boehm titration. The effect of ozonation pretreatment on the catalytic activity of MWCNT and the ozonation mechanism of oxalic acid in the presence of MWCNT were investigated. The results indicate that with the increasing pretreatment time, the atom ratio of oxygen to carbon and the number of surface acid groups on MWCNT increase, while the catalytic activity of MWCNT on ozonation of oxalic acid decreases, suggesting that the chemical characteristics of MWCNT mainly determine its catalytic activity on oxalic acid mineralization. The inhibition of tert-butyl alcohol on the degradation of oxalic acid is slight for pristine MWCNT catalytic ozonation and this inhibition trend becomes more obvious when MWCNT was pretreated by ozone. A free radical mechanism was proposed which involves both surface reactions and bulk reactions between the oxalic acid and active species.

Catalytic Ozonation of Oxalic Acid Using Carbon-Free Rice Husk Ash Catalysts

A highly efficient, carbon-free rice husk ash (RHA) has been successfully used as a catalyst in oxalic acid (OA) decomposition by combining with ozonation at pH 3. The catalyst was characterized using various analytical techniques. X-ray fluorescence (XRF) analysis showed that RHA catalyst contains SiO2 as a major constituent and MgO, P2O5, SO3, K2O, CaO, MnO2, Fe2O3, CuO, ZnO as minor constituents. X-ray diffraction (XRD) and EDX analysis consistently confirmed the presence of silica as a major constituent. Cold field scanning electron microscopic (FESEM) analysis revealed nonuniform particle size and the presence of external pores on the catalyst surface. Elemental analysis (EA) indicated that RHA contains negligible percentage of carbon content. Oxalic acid degradation as well as its TOC removal was studied at various physicochemical conditions. Adsorption and ozonation processes are not effective for oxalic acid and its TOC removal. The addition of RHA catalyst in the ozonation process caused 76.2% OA...