C2 Sites Research Articles

H-Bonds in Carbon Quantum Dot-anchored C3N5 to Boost Proton-Coupled Electron Transfer for Piezoelectric-Driven Hydrogen Peroxide Synthesis under Ambient Conditions.

Tuning proton-coupled electron transfer (PCET) is a promising strategy to boost the oxygen reduction reaction (ORR) for H2O2 synthesis, but the slow transmission rate of protons and electrons to active sites remains a significant bottleneck. To address this, we developed an H-bond-driven PCET process based on carbon quantum dotanchored C3N5 (CQDs-C3N5) for piezo-catalytic H2O2 synthesis. CQD-C3N5 exhibited a remarkable piezo-catalytic synthesis rate of 5025 μmol g⁻¹ h⁻¹ under ambient conditions. This efficiency is attributed to H-bonds between CQDs and C3N5, which accelerate PCET in the ORR. The piezoelectric-generated charges, from the dipole field of the C3N5 plane and protons in water, were rapidly transferred to the C rings of CQDs via H-bonds. This process facilitated the adsorption of oxygen onto C2 sites adjacent to carboxyl groups of CQDs, which in turn led to the formation of H2O2 through a rapidly protonated, indirect 2e- pathway. Additionally, a piezo-self-Fenton reaction system was constructed for oxytetracycline-rich wastewater purification, with effectively effects on chemical oxygen demand, antibiotic-resistant bacteria and antibiotic-resistant genes degradation. This study highlights the critical role of H-bond networks for tuning PCET in the ORR and provides a comprehensive understanding for the precise control of catalytic reaction kinetics through molecular structural engineering.

H‐Bonds in Carbon Quantum Dot‐anchored C3N5 to Boost Proton‐Coupled Electron Transfer for Piezoelectric‐Driven Hydrogen Peroxide Synthesis under Ambient Conditions

Tuning proton‐coupled electron transfer (PCET) is a promising strategy to boost the oxygen reduction reaction (ORR) for H2O2 synthesis, but the slow transmission rate of protons and electrons to active sites remains a significant bottleneck. To address this, we developed an H‐bond‐driven PCET process based on carbon quantum dotanchored C3N5 (CQDs‐C3N5) for piezo‐catalytic H2O2 synthesis. CQD‐C3N5 exhibited a remarkable piezo‐catalytic synthesis rate of 5025 μmol g⁻¹ h⁻¹ under ambient conditions. This efficiency is attributed to H‐bonds between CQDs and C3N5, which accelerate PCET in the ORR. The piezoelectric‐generated charges, from the dipole field of the C3N5 plane and protons in water, were rapidly transferred to the C rings of CQDs via H‐bonds. This process facilitated the adsorption of oxygen onto C2 sites adjacent to carboxyl groups of CQDs, which in turn led to the formation of H2O2 through a rapidly protonated, indirect 2e− pathway. Additionally, a piezo‐self‐Fenton reaction system was constructed for oxytetracycline‐rich wastewater purification, with effectively effects on chemical oxygen demand, antibiotic‐resistant bacteria and antibiotic‐resistant genes degradation. This study highlights the critical role of H‐bond networks for tuning PCET in the ORR and provides a comprehensive understanding for the precise control of catalytic reaction kinetics through molecular structural engineering.

Local control of S atoms on the Co-SACs for effective activation of PMS and degradation imidacloprid: Mechanism insights and toxicity evaluation.

Imidacloprid (IMI), as an emerging pollutant, is frequently detected in pesticide wastewater. Cobalt-based single-atom catalysts (Co-SACs) doped with sulfur atoms can serve as an efficient strategy to activate peroxymonosulfate (PMS) and degrade organic pollutants. The paper employed density functional theory and computational toxicology to deeply explore the mechanism and ecotoxicity of IMI when S atoms were introduced into Co-SACs for PMS activation. The result demonstrated that PMS can be preferentially decomposed into SO4•-, HO•, and 1O2 based on Co-S4-C0 active-center. It exhibited the most positive charge (+0.91 e-), highest electron transfer (0.84 e-), most negative adsorption energy (Eads = -53.85 kcal/mol), and longer O-O bond (1.48 Å). In the degradation processes of IMI, HO•-addition at the C2 sites and HO•-abstract at the H6 sites had the lowest Gibbs free barrier with 6.64 kcal/mol and 6.22 kcal/mol, respectively. Hydroxylation products were readily formed. Route 3 and 7 were the formation pathways of important experimental intermediates (PC3-4). Eco-toxicity assessment showed that most degradation products were completely harmless to aquatic toxicity. PC1-2, PC1-2, PC3-1, PC3-3, PC4-1 and PC4-2 showed similar and higher mutagenicity and bioaccumulation factors to the IMI. Therefore, Route 1, 3 and 4 contributed to the potential health risks. This study not only elucidated the atomic level relationship between PMS and Co-SACs, but also contributed to understanding the detailed degradation mechanism of IMI and the ecotoxicity of TPs. The finding provides theoretical support for environmental impacts of pesticide wastewater during advanced oxidation treatments.

Effect of Fuels on Structure, Morphology, and Spectroscopy of Combustion-Synthesized Y2O3:Eu3+ Nanoparticles: Towards Applications in Optoelectronic Devices and Biomedicine

Eu3+ ion doped yttria nanoparticles (Y2O3:Eu3+ NPs) were synthesized by a combustion method using urea (U), glycine (G), and ethylenediaminetetracetic acid (E) as fuels. Combustion parameters including adiabatic flame temperature and emitted heat, were calculated and found to increase with the fuel molecular weight. XRD pattern confirmed a body-centered cubic (BCC) phase with the Ia3 space group where Eu³⁺ ions occupied both C2 and S6 sites. Y2O3:Eu3+ NPs prepared with higher molecular weight fuels, exhibited the superior photoluminescence (PL) of the orange-red (O-R) bands. PL spectra revealed the dominant 5D0→7F2 transitions were driven by the energy transfer process from S6 sites to C2 sites via electric multipolar interactions. Chromaticity parameters confirmed the potential of these Y2O3:Eu3+ NPs for optoelectronic applications, with the strong luminescence in the O-R region, making them suitable for biomedical fluorescence imaging.

Solid-solution Er:(Sc,Y)2O3 transparent ceramics: Optical spectroscopy, inhomogeneous line broadening, C3i sites and mid-infrared laser operation

Rare-earth-doped transparent sesquioxide laser ceramics enable engineering of their gain bandwidths via solid-solution compositions exhibiting a strong inhomogeneous spectral line broadening. We report on a detailed spectroscopic study and the first mid-infrared laser operation of Erbium-doped yttria-scandia, (ScxY1−x)2O3, ceramics fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. The effect of the Sc fraction on the spectral and kinetic properties of Er3+ emission around 2.8 μm owing to the 4I11/2 → 4I13/2 is revealed. The inhomogeneous spectral line broadening leading to merging of individual Stark sub-levels of Er3+ multiplets is evidenced by low-temperature spectroscopy. An original method of quantifying the distribution of dopant Er3+ ions over C2 and C3i symmetry sites in the cubic bixbyite structure is suggested based on the transition probabilities derived by the Judd-Ofelt theory. In the parent Er:Y2O3 ceramic, the Er3+ ions nearly follow the ideal distribution with 3/4 of ions residing in C2 sites, and Sc addition skews it in favor of C3i sites. A continuous-wave Er:(Sc,Y)2O3 ceramic laser generated 312 mW at 2716 nm with a slope efficiency of 18.6 % and a laser threshold of 128 mW.

Luminescence and Faraday rotation properties of Tb2O3 and Tb:Y2O3 single crystals

Heavily-doped and fully concentrated 2.78 % Tb:Y2O3 and Tb2O3 single crystals with high optical quality and very low levels of impurities have been grown and studied for their luminescence and Faraday rotation properties. Absorption, emission and fluorescence decay measurements performed vs excitation wavelength and temperature and their confrontation with Judd-Ofelt and crystal-field calculations show the contributions of two types of luminescent centers: dominant ones with a 5D4 emission lifetime of 23 μs corresponding to coupled near-neighbor Tb3+ ions, all in C2 symmetry sites, and minority ones with a 5D4 emission lifetime of about 2 ms corresponding to coupled Tb3+ ions in C2 and C3i near-neighbor symmetry sites. Faraday rotation measurements confirm Tb2O3 as the Tb-based Faraday crystalline material with the largest ever measured Verdet constant, at all temperatures and from the visible to the near-infrared. They also show that the dominant luminescent centers contribute more particularly to this large Verdet constant thanks to a favorable crystal-field splitting of their 7F6 ground multiplet and also to the contributions of both types of spin-allowed and spin-forbidden 4f-5d absorption bands.

Multiscale Computational Study of Cellulose Acetate-Water Miscibility: Insights from Molecularly Informed Field-Theoretic Modeling.

Cellulose acetate (CA), a prominent water-soluble derivative of cellulose, is a promising biodegradable ingredient that has applications in films, membranes, fibers, drug delivery, and more. In this work, we present a molecularly informed field-theoretic model for CA to explore its phase behavior in aqueous solutions. By integrating atomistic details into large-scale field-theoretic simulations via the relative entropy coarse-graining framework, our approach enables efficient calculations of CA's miscibility window as a function of the degree of substitution (DS) of cellulose hydroxyl groups with acetate side chains. This allows us to capture the intricate phase behavior of CA, particularly its unique miscibility at intermediate substitution, without relying on experimental input. Additionally, the model directly probes CA solution behavior specific to the relative DS at C2, C3, and C6 alcohol sites, providing insights for the rational design of water-soluble CA for diverse applications. This work demonstrates a promising integration of molecularly informed field theories, complementing wet-lab experimentation, for engineering the next-generation polymeric materials with precisely tailored properties.

Theoretical analysis of naproxen reaction with sulfate and hydroxyl radicals in the aqueous phase: Investigating reactive sites and reaction kinetics

In this study, we have utilized theoretical calculations to predict the reaction active sites of naproxen when reacting with radicals and to further study the thermodynamics and kinetics of the reactions with ·OH and SO4−·. The evidence, derived from the average local ionization energy and electrostatic potential, points to the naphthalene ring as the preferred site of attack, especially for the C2, C6, C9, and C10 sites. The changes in Gibbs free energy and enthalpy of the reactions initiated by ·OH and SO4−· ranged between −19.6 kcal/mol - 26.3 kcal/mol and −22.3 kcal/mol −18.5 kcal/mol, respectively. More in-depth investigation revealed that RA2 pathway for ·OH exhibited the lowest free energy of activation, suggesting this reaction is more inclined to proceed. The second-order rate constant results indicate the ·OH attacking reaction is faster than reactions initiated by SO4·-, yet controlled by diffusion. The consistency between theoretical findings and experimental data underscores the validity of this computational method for our study.

Electronic and Molecular Adsorption Properties of Pt-Doped BC6N: An Ab-Initio Investigation.

In the last two decades, significant efforts have been particularly invested in two-dimensional (2D) hexagonal boron carbon nitride h-BxCyNz because of its unique physical and chemical characteristics. The presence of the carbon atoms lowers the large gap of its cousin structure, boron nitride (BN), making it more suitable for various applications. Here, we use density functional theory to study the structural, electronic, and magnetic properties of Pt-doped BC6N (Pt-BC6N, as well as its adsorption potential of small molecular gases (NO, NO2, CO2, NH3). We consider all distinct locations of the Pt atom in the supercell (B, N, and two C sites). Different adsorption locations are also considered for the pristine and Pt-doped systems. The formation energies of all Pt-doped structures are close to those of the pristine system, reflecting their stability. The pristine BC6N is semiconducting, so doping with Pt at the B and N sites gives a diluted magnetic semiconductor while doping at the C1 and C2 sites results in a smaller gap semiconductor. We find that all doped structures exhibit direct band gaps. The studied molecules are very weakly physisorbed on the pristine structure. Pt doping leads to much stronger interactions, where NO, NO2, and NH3 chemisorb on the doped systems, and CO2 physiorb, illustrating the doped systems' potential for gas purification applications. We also find that the adsorption changes the electronic and magnetic properties of the doped systems, inviting their consideration for spintronics and gas sensing.

Spectroscopy of thulium ions in solid-solution sesquioxide laser ceramics: Inhomogeneous spectral line broadening, crystal-field engineering and C3i sites

We present a detailed spectroscopic study of Tm3+ ions in stoichiometric and “mixed” (solid-solution) cubic (C-type, sp. gr. Ia3‾) sesquioxides R2O3 (RY, Lu, Sc or their mixture), with the goal of developing broadband-emitting gain media for ultrafast lasers at ∼2 μm. Evidence of a linear variation (increase) of the crystal-field strength when decreasing the ionic radius of the host-forming cation R3+ in the isostructrural R2O3 series is presented. The crystal-field splitting of Tm3+ multiplets is determined for C2 sites and justified using a barycenter plot, and the first evidence of C3i Tm3+ species is presented. A remarkable inhomogeneous spectral broadening for compositionally “mixed” sesquioxides (in particular with Sc3+) with respect to the parent compounds is revealed at low temperatures. It is proven that binary and ternary “mixed” R2O3 compounds form substitutional solid-solutions with a mixing of the host-forming cations at the atomic level. The stimulated-emission and gain cross-sections for the 3F4 → 3H6 Tm3+ transition are determined. Guidelines for material engineering of Tm3+-doped gain media for mode-locked 2-μm lasers are also provided.

Inhomogeneous spectral line broadening and site distribution in “mixed” Er:(Sc,Y)2O3 laser ceramics

Erbium-doped “mixed” yttria-scandia (ScxY1-x)2O3 transparent laser ceramics were fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. Their absorption and mid-infrared emission properties were studied. The addition of Sc3+ induces a strong inhomogeneous spectral line broadening, modifies the crystal field and affects the distribution of Er3+ ions over C2 and C3i symmetry sites. Due to their broadband emission properties, Er:(ScxY1-x)2O3 ceramics are appealing for 2.8-μm lasers.

Coordinatively unsaturated single-atom Cu catalysts with enhanced catalytic activity for furfural upgrading

The regulation of coordination number of metal single-atom (SA) sites is important and effective to tailor their catalytic performances. Herein, we report a novel defect-induced strategy for the fabrication of Cu SAs with unsaturated coordination configurations (Cu1C2). During the synthesis, polyvinyl pyrrolidone is employed to stabilize atomic Cu nodes and generate pores in adjacent areas. Systematical characterizations indicate the atomic distribution of Cu on C2 sites at the edge of pores in carbon support. The unsaturated coordination configurations and edge effect of the Cu1C2 moieties endow it with asymmetric geometry and shortened Cu-C bond length, leading to polarized charge distributions and up-shifted total density of states towards the Fermi level, which could facilitate O2 activation and lower oxidative coupling barriers. Impressively, Cu1C2@C exhibits superior catalytic performances in the oxidative coupling of furfural with isopropanol into 4-(2-furyl)-buten-2-one (a typical C8 biofuel intermediate), outperforming the Cu1C4@C counterpart.

Atmospheric degradation mechanism of anthracene initiated by OH•: A DFT prediction

Density functional theory (DFT) calculations at the M06-2X/def2-TZVP level have been employed to investigate the atmospheric oxidation mechanism of anthracene (ANT) initiated by HO•. Direct hydrogen atom abstraction from the ANT using HO• takes place hardly at ambient conditions while addition of HO• to the C1, C2, and C4 sites are thermodynamically and kinetically more advantageous. The addition reactions are controlled by the aromaticity and the kinetic trends were justified by resonance stabilization energies. The rate constants were calculated by using the Rice-Ramsperger-Kassel-Marcus (RRKM) and canonical transition state theory (CTST) methods in conjugation with zero curvature tunneling (ZCT). The overall RRKM-bimolecular rate constant at ambient conditions is 6.72 × 10−12 cm3 molecule−1 s−1, is negatively dependent on the temperature and can be expressed as k250−3501bar=3.92×10−14exp(1534.9T). Contribution of the AD-C4 path in the overall reaction is about 70–80%, implying that the dependence of overall rate constant on pressure can be ignored. The kinetic data exhibit that the ANT is degraded during its long-range transport in the atmosphere and cannot be classified as persistent organic pollutants.

Structural and optical characterisation of silanised Dy-doped-Gd2O3 NPs.

In this work, we studied the optical properties of Dy-doped Gd2O3 nanoparticles (NPs) before and after their APTES functionalisation. We obtained luminescent Dy@Gd2O3 NPs (0.5, 1, and 5% mol) using a modified polyol method. Our work describes their detailed structural analysis using FT-IR, XRD, HRTEM, TGA and XAS techniques. The results show that these systems present a crystalline structure with a body-centred cubic cell and particle sizes of 10 nm. The dopant position was inferred as substitutional, through XAS analysis at the M4,5-edges of Gd and Dy and K-edge of O, and in C2 sites, based on photoluminescence studies. There was sensitization of the luminescence by the matrix as shown by the emission increase of the hypersensitive transition (6F9/2 → 6H13/2, 572 nm) and also a broadband appears around 510 nm attributed to defects in Gd2O3. An enhanced emissive lifetime of 398 μs was found for the sample doped at 1%. We functionalised the Dy@Gd2O3 (at 1%) NPs with 3-aminopropiltrietoxisilane (APTES) for further application as a biomarker sensor. We found that these NPs conserved their luminescence after adding the surface agent (avoiding quenching effects) making them potential materials for biosensing.

Theoretical study on the degradation mechanism of propranolol in aqueous solution initiated by hydroxyl and sulfate radicals

In this paper, density functional theory (DFT) calculation was carried out to explore hydroxyl (•OH) and sulfate radicals (SO4•-)-initiated oxidative degradation of propranolol (PRO) in an aqueous solution. It was found that the most favorable pathways for the reactions between PRO and •OH are •OH addition (ADD) reactions related to C1, C2, and C4 sites of PRO and hydrogen atom abstraction (HAA) channels involving C10-H, C11-H, and C13-H bonds. The plausible subsequent reactions of the favorable initial intermediates include hydroxylation, naphthalene ring cleavage, ether bond and CN bonds breakage, and their combination. SO4•- was found to have stronger oxidizing performance than •OH in the aqueous degradation of PRO. Single electron transfer (SET) reaction between PRO and SO4•- is not feasible. Water molecules and dissolved oxygen in water participate in aqueous degradation of PRO.

Regioselective Synthesis of 1‐Cyano‐3‐arylindolizines: Construction of Pyrroles via DDQ‐Mediated Ring Closure of Cyclopropyl Pyridines

AbstractA modular approach to a wide range of 1‐cyano‐3‐(hetero)arylindolizines through aldol‐cyclopropanation‐oxidative cycloisomerization is described where DDQ was utilized for the regioselective synthesis of the pyrrole units from cyclopropyl pyridines for the first time. A key to success is regioselective oxidation of benzylic position by DDQ, which enabled us to access to one regioisomer out of two possible ones. Homo‐dimerization at the C2, C5, or C7 sites of indolizines in the presence of DDQ has been discovered for the first time as well.magnified image

Afterglow-Suppressed Lu2O3:Eu3+ Nanoscintillators for High-Resolution and Dynamic Digital Radiographic Imaging.

Lu2(1-x)Eu2xO3 nanoscintillators (x = 0.005, 0.01, 0.03, 0.05, 0.07, and 0.10) with red emission were synthesized by a coprecipitation method. It is found that their photo- and radioluminescence intensities increase with increasing Eu3+ concentration until x = 0.05. According to their concentration-dependent luminescence intensity ratios (I610(C2)/I582(S6)), the existing energy transfer from Eu3+(S6) (occupying S6 sites) to Eu3+(C2) (occupying C2 sites) can be confirmed. Based on the spectral data and density functional theory (DFT) calculations, the origin of Lu2O3:Eu3+ persistent luminescence at low concentration might be related to the tunneling processes between Eu3+ (occupying C2 and S6 sites) and oxygen interstitials (Oi×). After dispersing afterglow-suppressed Lu2O3:Eu3+ nanoscintillators into polymethyl methacrylate (PMMA) polymer-acetone solution, flexible PMMA-Lu2O3:Eu3+ composite films with high thermal stability and radiation resistance were fabricated by a doctor blade method. As the flexible composite film was used as an imaging plate, static X-ray images with high spatial resolution (5.5 lp/mm) under an extremely low dose of ∼1.1 μGyair can be acquired. When a watch with a moving second hand was used as an object, the dynamic X-ray imaging can be realized under a dose rate of 55 μGyair·s-1. Our results demonstrate that Lu2O3:Eu3+ nanoscintillators can be regarded as candidate materials for dynamic digital radiographic imaging.

Coupling of N-Doped Mesoporous Carbon and N-Ti3 C2 in 2D Sandwiched Heterostructure for Enhanced Oxygen Electroreduction.

2D heterostructures provide a competitive platform to tailor electrical property through control of layer structure and constituents. However, despite the diverse integration of 2D materials and their application flexibility, tailoring synergistic interlayer interactions between 2D materials that form electronically coupled heterostructures remains a grand challenge. Here, the rational design and optimized synthesis of electronically coupled N-doped mesoporous defective carbon and nitrogen modified titanium carbide (Ti3 C2 ) in a 2D sandwiched heterostructure, is reported. First, a F127-polydopamine single-micelle-directed interfacial assembly strategy guarantees the construction of two surrounding mesoporous N-doped carbon monolayers assembled on both sides of Ti3 C2 nanosheets. Second, the followed ammonia post-treatment successfully introduces N elements into Ti3 C2 structure and more defective sites in N-doped mesoporous carbon. Finally, the oxygen reduction reaction (ORR) and theoretical calculation prove the synergistic coupled electronic effect between N-Ti3 C2 and defective N-doped carbon active sites in the 2D sandwiched heterostructure. Compared with the control 2D samples (0.87-0.88V, 4.90-5.15 mA cm-2 ), the coupled 2D heterostructure possesses the best onset potential of 0.90V and limited density current of 5.50 mA cm-2 . Meanwhile, this catalyst exhibits superior methanol tolerance and cyclic durability. This design philosophy opens up a new thought for tailoring synergistic interlayer interactions between 2D materials.

Fabrication and luminescent properties of uranium doped Y2O3 transparent ceramics by sintering aid combinations

Uranium doped Y2O3 transparent ceramics with ZrO2 and La2O3 as sintering aids, Ca2+ as charge compensator were successfully fabricated via a vacuum solid-state reactive sintering for the first time. The obtained ceramic showed a pure cubic Y2O3 phase structure and homogeneous microstructure with the average grain size of 20 μm. The in-line transmittance of the obtained U: Y2O3 reached 78% at 1300 nm. And the cut-off wavelength shifted from 250 nm to 520 nm, which was ascribed to the absorption of uranate ions. XPS and photoluminescence study confirmed uranium stabilizes as +6 oxidation state in the form of UO66−. The decay curve shows two lifetime values indicating that uranate ions are not homogeneously distributed in Y2O3 and it has two different environments due to its stabilization at both C2 and S6 sites. The lifetime population analysis shows that most UO66− ions were located at the non-centrosymmetric C2 site. The experimental results are helpful in designing Y2O3 based optoelectronic material as well exploring it for uranium studies.

Probing of sequential atmospheric degradation of chlorine radical initiated 1,8-cineole in the presence of O2 and NO radical with the emission of secondary pollution

1,8-cineole is an essential monoterpene cyclic ether which is released into the troposphere by many types of plants. It interacts with several atmospheric oxidants because of which is removed from the troposphere via oxidation. The oxidation of 1,8-cineole with Cl radical and the subsequent addition of atmospheric O2 and NO radical with the intermediates are studied using the quantum chemical method. Further, the thermodynamic parameters of 1,8-cineole, such as enthalpy and Gibbs free energy are calculated for all initial and subsequent reactions to facilitate perspicacity. The dissociation and formation of chemical bonds during H abstraction from 1,8-cineole at C2, C6, and C8 sites are described using Mayer bond order analysis. The reaction force analysis demonstrates that the structural rearrangement is dominant with the yield percentages of 85%, 50.80%, and 96.9% over electron reordering with the yield percentages of 15%, 49.19%, and 3.03% respectively in the H abstraction reaction of 1,8-cineole. In the temperature range of 278–350 K, the total CVT/SCT rate constant is calculated to be 2.94 × 10−12 cm3/molecule/sec, which is consistent with the experimentally available value of 2.2 × 10−10 cm3/molecule/sec. At 298 K, branching ratios of rate constant of alkyl radical intermediates I1A, I1B, and I1C are calculated with the percentage of 42.19%, 21.52%, and 36.29% respectively, which suggest that the Cl addition to the C2 site contributes more to the total rate constant rather than the other two sites (C6 and C8). The lifetime of 1,8-cineole is calculated to be 5.2 weeks, implies that the 1,8-cineole may be readily destroyed in the atmosphere after it is released. Secondary pollutants formed from this degradation mechanism may be harmful to the environment and the living things.