Electrolytic control of hydrogen peroxide release from calcium peroxide in aqueous solution

Improvement of Fe(Ⅲ)/percarbonate system by molybdenum powder and tripolyphosphate: Co-catalytic performance, low oxidant consumption, pH-dependent mechanism

The homogeneous sodium percarbonate (SPC) systems are limited by narrow pH range, ineffective consumption of oxidant, and weak reusability of catalyst. Herein, molybdenum (Mo) powder and sodium tripolyphosphate (STPP) were selected to overcome these challenges. Sulfamethoxazole (SMX), as a model contaminant, was almost completely degraded in 60 min with higher removal rate (0.1367 min-1) than the Mo or STPP-absent system. In addition, Mo/STPP-Fe(Ⅲ)/SPC system was cost-effective in terms of oxidant consumption, requiring only 0.2 mM SPC. About activation mechanism, the main active species for SMX degradation was pH-dependent, with hydroxyl radical (·OH) as the dominant active species at pHi = 7 and ·OH, carbonate radical (CO3·-), and superoxide radical (O2·-) derived from a series of chain reaction at pHi = 10, respectively. Due to the generation of various electrophilic free radical, the system exhibited excellent performance towards electron-rich pollutants under a wide pH range. Furthermore, Mo exhibited excellent stability and reusability. SMX was degraded through hydroxylation, N-S cleavage, amino and sulfanilamide oxidation into intermediates whose toxicities were evaluated by Toxicity Estimation Software Tool (T.E.S.T.) software. This work provided new insights to Fe/SPC system towards high-efficiency and low consumption treatment of practical application.

The Degradation of Aqueous Oxytetracycline by an O3/CaO2 System in the Presence of HCO3-: Performance, Mechanism, Degradation Pathways, and Toxicity Evaluation

This research constructed a novel O3/CaO2/HCO3- system to degrade antibiotic oxytetracycline (OTC) in water. The results indicated that CaO2 and HCO3- addition could promote OTC degradation in an O3 system. There is an optimal dosage of CaO2 (0.05 g/L) and HCO3- (2.25 mmol/L) that promotes OTC degradation. After 30 min of treatment, approximately 91.5% of the OTC molecules were eliminated in the O3/CaO2/HCO3- system. A higher O3 concentration, alkaline condition, and lower OTC concentration were conducive to OTC decomposition. Active substances including ·OH, 1O2, ·O2-, and ·HCO3- play certain roles in OTC degradation. The production of ·OH followed the order: O3/CaO2/HCO3- > O3/CaO2 > O3. Compared to the sole O3 system, TOC and COD were easier to remove in the O3/CaO2/HCO3- system. Based on DFT and LC-MS, active species dominant in the degradation pathways of OTC were proposed. Then, an evaluation of the toxic changes in intermediates during OTC degradation was carried out. The feasibility of O3/CaO2/HCO3- for the treatment of other substances, such as bisphenol A, tetracycline, and actual wastewater, was investigated. Finally, the energy efficiency of the O3/CaO2/HCO3- system was calculated and compared with other mainstream processes of OTC degradation. The O3/CaO2/HCO3- system may be considered as an efficient and economical approach for antibiotic destruction.

Hydrogel-Impregnated Self-Oxygenating Electrospun Scaffolds for Bone Tissue Engineering

Bone defects resulting from trauma, disease, or aging present significant challenges in the clinic. Although biomaterial scaffolds for bone-tissue engineering have shown promising results, challenges remain, including the need for adequate mechanical strength and suitable bioactive agents within scaffolds to promote bone formation. Oxygen is a critical factor for successful bone formation, and low oxygen tension inhibits it. In this study, we developed gelatin methacryloyl (GelMA) hydrogel-impregnated electrospun polycaprolactone (PCL) scaffolds that can release oxygen over 3 weeks. We investigated the potential of composite scaffolds for cell survival in bone-tissue engineering. Our results showed that the addition of an increased amount of CaO2 nanoparticles to the PCL scaffolds significantly increased oxygen generation, which was modulated by GelMA impregnation. Moreover, the resulting scaffolds showed improved cytocompatibility, pre-osteoblast adhesion, and proliferation under hypoxic conditions. This finding is particularly relevant since hypoxia is a prevalent feature in various bone diseases. In addition to providing oxygen, CaO2 nanoparticles also act as reinforcing agents improving the mechanical property of the scaffolds, while the incorporation of GelMA enhances cell adhesion and proliferation properties. Overall, our newly developed self-oxygenating composite biomaterials are promising scaffolds for bone-tissue engineering applications.

An In Vitro Study of Local Oxygen Therapy as Adjunctive Antimicrobial Therapeutic Option for Patients with Periodontitis

Periodontitis is a common global disease caused by bacterial dysbiosis leading to tissue destruction, and it is strongly associated with anaerobic bacterial colonization. Therapeutic strategies such as oxygen therapy have been developed to positively influence the dysbiotic microbiota, and the use of oxygen-releasing substances may offer an added benefit of avoiding systemic effects commonly associated with antibiotics taken orally or hyperbaric oxygen therapy. Therefore, the oxygen release of calcium peroxide (CaO₂) was measured using a dissolved oxygen meter, and CaO₂ solutions were prepared by dissolving autoclaved CaO₂ in sterile filtered and deionized water. The effects of CaO₂ on planktonic bacterial growth and metabolic activity, as well as on biofilms of Streptococcus oralis and Porphyromonas gingivalis, were investigated through experiments conducted under anaerobic conditions. The objective of this study was to investigate the potential of CaO₂ as an antimicrobial agent for the treatment of periodontitis. Results showed that CaO₂ selectively inhibited the growth and viability of P. gingivalis (p < 0.001) but had little effect on S. oralis (p < 0.01), indicating that CaO₂ has the potential to selectively affect both planktonic bacteria and mono-species biofilms of P. gingivalis. The results of this study suggest that CaO₂ could be a promising antimicrobial agent with selective activity for the treatment of periodontitis.

Fe(II)-activated sodium percarbonate for improving sludge dewaterability: Experimental and theoretical investigation combined with the evaluation of subsequent utilization

Fe(II)-activated sodium percarbonate (SPC) was an emerging technology for enhancing the dewaterability of waste activated sludge, and its operational parameters were systematically explored. The results showed that after the treatment by 1.20 mmol/g VSS SPC and 1.44 mmol/g VSS Fe(II) at initial pH 3.0, the water content and specific resistance to filtration remained at 76.05 ± 0.36% and 2.57 ± 0.08 × 10¹² m·kg^-1, respectively. The acid condition was instrumental in sludge dewatering, whereas overdosing Fe(II) or SPC imposed adverse effect. The conversion of EPS fractions was examined to elucidate the underlying mechanism, which indicated that a coexisting oxidation/flocculation process accounted for the improvement of sludge dewaterability. The stronger oxidative ·OH degraded the hydrophilic compounds (proteins and carbohydrates) of tightly-bound extracellular polymeric substance and the dissolved multivalence iron promoted solid-liquid separation. Additionally, the theoretical analysis (DFT calculation) demonstrated that the oxygen- and nitrogen-containing groups of EPS resulted in high-water holding capacity of sludge. The difficulty of destroying hydrophilic functional groups followed C=O > C-N > C-O during oxidation process. Moreover, Fe(II)/SPC treatment performed well in coliforms inactivation and phytotoxicity reduction compared with different ·OH-based advanced oxidation processes for sludge conditioning.

Degradation of diclofenac sodium using Fenton-like technology based on nano-calcium peroxide

A nano-calcium peroxide (nCaO₂) powder with a purity of 89.1% was prepared using an improved traditional method. Then, the as-prepared nCaO₂ was used as the source of hydrogen peroxide (H₂O₂) for the Fenton-like degradation of diclofenac sodium (DCF). The results showed that nCaO₂ performed better for DCF removal when compared to nCaO₂ prepared by a conventional method and commercial calcium peroxide (CaO₂). Further experimental results indicated that 97.5% of DCF could be removed in 180 min at a nCaO₂/Fe²⁺-EDTA/DCF molar ratio of 16/8-8/1, which was more efficient than in the H₂O₂/EDTA-Fe²⁺/DCF and nCaO₂/Fe²⁺/DCF systems. The best removal rate of DCF was at pH 6.0, unlike previous claims that stated that the lower the pH in the buffer system, the better the degradation of DCF. In addition, the influence of water quality parameters, such as Cl^-, NO₃^-, SO₄^2-, HCO₃^-, and humic acid (HA), on DCF removal were evaluated. A free radical masking experiment revealed the existence of hydroxyl radical (OH), superoxide radical (O₂^-) and singlet oxygen (¹O₂), and indicated that the degradation of DCF was mainly due to oxidation caused by OH. Electron paramagnetic resonance (EPR) studies for different systems and different active oxygen species were carried out, and it was further confirmed that OH radicals have high intensity in the Fenton-like system based on nCaO₂. EPR results also showed that the addition of EDTA can promote the production of OH. According to the identification of the dominant reactive species and GC-MS, the possible theoretical DCF degradation pathways were proposed.

The performance of chlorobenzene degradation in groundwater: comparison of hydrogen peroxide, nanoscale calcium peroxide and sodium percarbonate activated with ferrous iron

The chlorobenzene (CB) degradation performances by various oxidants, including hydrogen peroxide (H₂O₂), nanoscale calcium peroxide (nCaO₂) and sodium percarbonate (SPC), activated with ferrous iron (Fe(II)) were investigated and thoroughly compared. The results showed that all tested systems had strong abilities to degrade CB. The CB removal rate increased with increasing dosages of oxidants or Fe(II) because the generation of reactive oxygen species could be promoted with the chemical dosages' increase. Response surface and contour plots showed that CB could achieve a better removal performance at the same H₂O₂ and Fe(II) molar content, but the Fe(II) dosage was higher than that of oxidants in the nCaO₂ and SPC systems. The optimal molar ratios of H₂O₂/Fe(II)/CB, nCaO₂/Fe(II)/CB and SPC /Fe(II)/CB were 5.2/7.6/1, 8/8/1, and 4.5/8/1, respectively, in which 98.1%, 98%, and 96.4% CB removals could be obtained in 30 min reaction. The optimal pH condition was around 3, while CB removal rates were less than 20% in all three systems when the initial pH was adjusted to 9. The oxidative hydroxyl radicals (HO•) and singlet oxygen (¹O₂) had been detected by the electron paramagnetic resonance test. Based upon the results of liquid chromatograph-mass spectrometer analysis, the pathways of CB degradation were proposed, in which ¹O₂ roles were elaborated innovatively in the CB degradation mechanism. The CB degradation performance was significantly affected in actual groundwater, while increasing the molar ratio of oxidant/Fe(II)/CB was an effective way to overcome the adverse effects caused by the complex of actual groundwater matrix.

Oxygen-generating smart hydrogels supporting chondrocytes survival in oxygen-free environments

Cartilage is one of our body's tissues which are not repaired automatically by itself. Problems associated with cartilage are very common worldwide and are considered the leading cause of pain and disability. Smart biomaterial or "Four dimensional" (4D) biomaterials has started emerging as a suitable candidate, which are principally three dimensional (3D) materials that change their morphology or generate a response measured at space and time to physiologic stimuli. In this context, the release of oxygen through hydrogels in contact with water is considered as 4D biomaterials. The objective of this study is to develop strategies to release oxygen in a sustainable and prolonged manner through hydrogels systems to promote chondrocytes survival in oxygen-free environment. The 4D biomaterials are engineered from gelatin methacryloyl (GelMA) loaded with calcium peroxide (CPO), which have the ability to generate oxygen in a controlled and sustained manner for up to 6 days. The incorporation of CPO into the hydrogel system provided materials with enhanced mechanical and porosity properties. Furthermore, the hydrogels promoted chondrocyte survival and reduced cell death under oxygen-free conditions.

Application of encapsulated magnesium peroxide (MgO2) nanoparticles in permeable reactive barrier (PRB) for naphthalene and toluene bioremediation from groundwater

One of the challenges in the petroleum hydrocarbon contaminated groundwater remediation by oxygen releasing compounds (ORCs) is to identify the remediation mechanism and determine the impact of ORCs on the environment and the intrinsic groundwater microorganisms. In this research, the application of encapsulated magnesium peroxide (MgO₂) nanoparticles in the permeable reactive barrier (PRB) for bioremediation of the groundwater contaminated by toluene and naphthalene was studied in the continuous flow sand-packed plexiglass columns within 50 d experiments. For the biodiversity studies, next generation sequencing (NGS) of the 16S rRNA gene was applied. The results showed that naphthalene was metabolized (within 20 days) faster than toluene (after 30 days) by microorganisms of the aqueous phase. By comparing the contaminant removal in the biotic (which resulted in the complete contaminant removal) and abiotic (around 32% removal for naphthalene and 36% for toluene after 50 d) conditions, the significant role of microorganisms on the decontamination process was proved. Furthermore, the attached microbial communities on the porous media were visualized by scanning electron microscopy (SEM). Microbial community structure analysis by NGS technique revealed that the microbial species which were able to degrade toluene and naphthalene such as P. putida and P. mendocina respectively were stimulated by addition of MgO₂ nanoparticles. The presented study resulted in a momentous insight into the application of MgO₂ nanoparticles in the hydrocarbon compounds removal from groundwater.