Kinetics of UV-Assisted and MnO2 Photocatalysed Degradation of Dinaphthophenazine

Kinetics of UV-Assisted and MnO2 Photocatalysed Degradation of Dinaphthophenazine | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Kinetics of UV-Assisted and MnO2 Photocatalysed Degradation of Dinaphthophenazine Kelvin Kimaru, Seth Otieno Osumba, Josiah Ouma Omolo, John Onyango Adongo This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8658954/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Apr, 2026 Read the published version in Reaction Kinetics, Mechanisms and Catalysis → Version 1 posted You are reading this latest preprint version Abstract The treatment of the dye-contaminated wastewater using ultraviolet (UV)-induced photodegradation, metal oxides and photocatalysts continues to be investigated by chemists towards improving dye-pollutant remediation technologies for environmental protection. In this study, a Dinaphthophenazine (DNPz.) textile dye was subjected to degradation experiments to characterise its degradation rates and highlight the photocatalytic degradation effect of manganese (IV)oxide (MnO 2 ) by comparing the kinetics of UV-induced degradation against MnO 2 – catalyzed photodegradation. Kinetic experiments were conducted by acquiring time-dependent wavelength scan absorption spectra at intervals using double-beam UV-Vis-NIR spectroscopy and a photo-cell setup. A multicurve kinetic profile plot analysis of the three experiments: exposure of DNPz to UV irradiation [DNPz.+UV irrad.], exposure of DNPz to MnO 2 only [DNPz.+MnO 2 ], and the exposure of DNPz to a similar dose of MnO 2 in the presence of UV 254 nm irradiation revealed a decrease in absorbance related to the DNPz molecule over time, indicating degradation of DNPz molecules under acidic conditions, pH 5.0 and at room temperature. A comparative analysis of the pseudo-1 st -Order degradation rates shows that exposure of DNPz to MnO 2 in the presence of UV irradiation gave the most significant average rate constant, which is about 9.65 times faster than in the case of the UV-assisted photodegradation based on kinetics monitored using DNPz’s Lambda max. absorptions at 621 nm. This is due to the photocatalytic effect of MnO 2 . The exposure to MnO 2 showed a marked increase in DNPz degradation rate that was about 3.31 times that of the average photodegradation rate recorded by exposure to UV 254 nm irradiation only. These results show that MnO 2 in the presence of UV 254 nm can significantly enhance the degradation of the DNPz textile dye. Photodegradation UV-irradiation Dinaphthophenazine Manganese (IV)oxide Photocatalytic effect Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Article Highlights Exposure of dinaphthophenazine textile dye to UV irradiation causes its photodegradation based on absorption measurements. Manganese (IV) oxide can degrade dinaphthophenazine dye at a higher rate than UV exposure. The degradation rate of dinaphthophenazine is significantly enhanced upon exposure to UV irradiation in the presence of MnO 2 . This demonstrates its photocatalytic effects. Introduction Catalytic photo-oxidation is one of the most effective strategies, which could completely convert organic pollutants into harmless products like carbon dioxide and water. Currently, there are a number of metal oxides known that play roles in photocatalytic degradation strategies and technologies that exploit oxidation mechanisms to achieve promising degradation rates for organic pollutant materials [ 1 – 4 ]. In recent years, a number of researchers have shown that manganese oxides and their composites can function as effective adsorbents and catalysts for remediating organic pollutants [ 5 – 7 ]. Dinaphthophenazine (DNPz) is a derivative of phenazine, a dibenzoannulated pyrazine, a parent substance in many dyestuffs. The DNPz molecule constitutes a class of artificial water-soluble organic compounds commonly applied in textile dying. The DNPz synthetic dyes are derived from aromatic compounds containing amine functional groups as the precursor compounds. They are part larger class of synthetic Vat dyes, the majority of which are poly-condensed aromatic carbonyl compounds, and as such, they bear a close resemblance to anthraquinone dyestuffs 8,9 . When present in industrial textile wastewaters as residues, they can accumulate as environmentally hazardous pollutants [ 10 , 11 ]. Despite their significant economic advantages in the textile industry, some of their synthetic precursors are associated with potentially adverse health risks to humans, such as skin cancers, lung cancers, allergies, neurocognitive effects and formation of haemoglobin adduct(s), among other deleterious health effects which have been linked to medium- or long- term exposures or ingestion [ 12 ]. In this study, a derivative of DNPz textile organic dyestuff compound, with the trade name of Vat blue 6, was subjected to photodegradation experiments in the laboratory. Three experiments involving exposure of DNPz to UV-irradiation only [DNPz.+ UV only], exposure to MnO 2 [DNPz.+ MnO 2 only], and exposure to MnO 2 in presence of UV-irradiation [DNPz.+ MnO 2 + UV irradiation.] were set up to investigate the photodegradation of the NPz molecule. Time-dependent wavelength scan absorption spectra were acquired during the photodegradation reactions using UV-Visible spectroscopy. The absorption spectra were plotted in graphs and charts as a function of time to characterise and evaluate the rates of decrease in NPz concentrations resulting from the exposure conditions. In all three kinetic experiments [DNPz.+ UV irrad], [DNPz.+ MnO 2 only], [(DNPz) + MnO 2 + UV irradiation.], a gradual decrease in the absorption spectra over the same time interval, characterising the degradation reactions, was observed. Varying average first-order photodegradation rate constants were recorded. Kinetic analyses of the spectroscopic data showed that exposure of DNPz to MnO 2 only and MnO 2 in the presence of UV irradiation gave significantly higher average first-order photodegradation rate constants as opposed to exposure to UV-irradiation only. Experimental Reagents : Analytical grade (% purity > 99%) versions of manganese (VI) oxide (acidified), 70% acetone and deionised water (DI) were acquired from Kobian distributors limited. A dinaphthophenazine (DNPz) dye [Trade Name: Blue K fluorescent dye, Vat-Blue 6 (Mwt. = 511.31 g/mol) IUPAC Name: 7,16-dichloro-6,15-dihydrodinaphtho[2,3-a:2',3'-h]phenazine-5,9,14,18-tetraone Mol. Formula: C 28 H 12 Cl 2 N 2 O 4 ] was purchased from Gala Textile Ltd, Nairobi, Kenya. Instrumentation Shimadzu model (AUY 120) analytical balance was used for weight measurements. Spectral data acquisition was done with a double-beam UV-Visible-Near IR spectrometer (UV-VIS K9000 model). Ultraviolet irradiation experiments were conducted using with UV-lamp (UVI-TEC model). A Texas Instruments LED digital watch was used as the timer for the spectra acquisition degradation experiments. Method In this study, the degradation experiments were optimised and conducted in a photocell chamber. To investigate the effect of UV radiation on DNPz. degradation, 3.5 mL of 50 mg/L of DNPz dye in 70% acetone was exposed directly to UV light of 48 W/cm 2 , 254 nm in the kinetic experiment labelled [DNPz. dye + UV irrad. only] and absorption spectra acquired at time intervals of 0 min., 10 min., 20 min., 30 min., 50 min., 1hr.10 min, 1hr.30 min., 2hr. 30min. To establish the effect of MnO 2 on DNPz dye degradation, 1 mL drop of 5 mg/L of MnO 2 in DI water was added to 2.5 mL of 50 mg/L of DNPz dye in 70% acetone in the kinetic experiment [DNPz. dye + MnO 2 only] in the dark. The degradation of the dye was monitored using periodic wavelength scan UV-Vis-NIR absorption spectra acquired at similar intervals as in the case of UV irradiation only. To further investigate the photocatalytic effect of MnO 2 on the degradation of DNPz dye, the kinetic experiment [DNPz. dye + MnO 2 + UV irrad.] was a setup and spectra acquired at similar time intervals for comparison reasons. The kinetic profiles for the three experiments were graphed in multicurve plots, box charts, OriginPro®v.9.0. Results and Discussion UV-VIS-Near-IR Characterisation of DNPz Dye and its Photodegradation Figure 1 a below shows the UV-Vis-NIR absorption spectra of the dinaphthophenazine (DNPz) textile dye (in Orange and blue). The wavelength scans span the range 1100 nm to 250 nm. The spectrum in red was obtained from a freshly prepared sample of manganese(IV) oxide (MnO 2 ) in aqueous solution. These plots act as important spectral references for monitoring the changes in concentration of the absorbing species (or chromophores) over time to determine the kinetic profiles of degradation, reaction rates, and to characterise catalytic activities [ 13 ]. The MnO 2 spectrum in red does not show any absorption that coincides with the broad absorption band recorded for DNPz (in Orange) and DNPz+MnO 2 (in blue) within the visible and near IR regions. It can be observed in Fig. 1 a that the textile organic dye molecule NPz exhibits a very broad absorption across the ultraviolet, visible and near-IR ranges with a maximum absorption in the visible range at 621 nm. The absorption of DNPz dye is also characterised by a shoulder peak at 760 nm. The extensive conjugation in the DNPz contributes to the broad absorption observed in its UV-Vis-NIR spectra. Figure 1 b shows the first-order derivative spectra from the respective spectra in Fig. 1 a. It confirms further that the derivatives are at zero at 760 nm and at 621 nm for the corresponding peaks identified in Fig. 1 a. It can also be noted from Fig. 1 a that there is some absorption in the near IR region 1050–1100 nm. Figure 2 depicts UV-Vis-NIR wavelength scan absorption spectra acquired over time. They characterise UV-Assisted photodegradation of the DNPz molecule based on the observed decrease in absorbance over time upon exposure of DNPz to UV 254 nm irradiation. The inset figure shows all the spectra acquired during the [DNPz.+UV irrad.] kinetic experiment within the near-IR region highlighted more clearly. The general decrease in absorption (or concentration) over time, evidently observed in the spectra, characterises UV-assisted photodegradation of DNPz molecules. A similar trend of decreasing absorbance over time is observed at the Lamba max. of 621 nm and the shoulder peak at 760 nm. Kinetics of DNPz Degradation and Photocatalytic Effect of MnO Figure 3 shows the spectra derived from three kinetic experimental setups: [DNPz.+UV irrad.] (in Fig. 3 a,b), [DNPz.+MnO 2 ] (in Fig. 3 c,d), and [NPz.+UV irrad.+MnO 2 ] (in Fig. 3 e,f) that we conducted to evaluate and characterise the photodegradation rates of the NPz dye under different conditions. In all three experiments, the initial concentration of NPz was held at 0.1M while studying the effect of UV irradiation, exposure to MnO 2 and exposure to MnO 2 coupled with UV irradiation. The absorption bands within the visible region, λ max. value at 621 nm and the shoulder peak at 760 nm, were used to spectroscopically characterise and compare the degradation rates based on the changes in absorbance values, d Abs . (reflecting changes in concentration) among the three categories of experiments conducted within similar time intervals (0 min. to 2hr. 30 min.). In all three experiments, a decrease in absorbance was observed, but at varying rates. The difference in absorbance values recorded just at the start of the experiment (Abs. t i = 0 min.) and at the end of the experiment (Abs. t f = 2hr. 30min.) was used to compute the overall change in absorbance (d Abs.), for each experiment as shown in all the charts in Fig. 3 . All the d Abs . values are summarised in Table 1 . The calculated ratios, b/a and c/a, in the last column indicate the incremental effects of MnO 2 and UV irradiation (in the presence of MnO 2 ) on the photodegradation rates of DNPz dye.. Table 1 Comparison of change in absorbance (d Abs .) values from the kinetic experiments: [DNPz.+UV irrad.], [DNPz.+MnO 2 ], and [DNPz.+UV irrad.+MnO 2 ] Spectroscopic Absorption Bands in the Visible region Change in Abs. (d Abs.) (Initial Abs. t i = 0 min – Final Abs. t f = 2hr.30min.) Incremental ratio [DNPz.+UV irrad.] a [DNPz.+MnO 2 .] b [DNPz.+UV irrad.+MnO 2 ] c b/a ; c/a Abs. band, (λ max .) at 621 nm 9.0 x 10 − 3 2.8 x 10 − 2 4.8 x 10 − 2 3.11 ; 5.33 Abs. band at 760 nm 1.2 x 10 − 2 1.6 x 10 − 2 2.0 x 10 − 2 1.33 ; 1.66 It can be noted from Table 1 that the greatest change in concentration (based on absorbance data) was recorded from the [DNPz.+UV irrad.+MnO 2 ], where both UV irradiation and MnO 2 were used to cause degradation. The least change in concentration for the same period of time was observed in the [DNPz.+UV irrad.] experiment, where only UV irradiation was used to degrade DNPz molecules. It was also observed that MnO 2 caused some degradation of the DNPz molecules, even without UV irradiation in the [DNPz.+MnO 2 ] kinetic experiment. The incremental ratios are calculated with respect to the d Abs . values of [DNPz.+UV irrad.] The experiment revealed that MnO 2 increased the d Abs . value by a factor of about 3.11, while MnO 2 in the presence of UV irradiation increases it by about 5.33 based on the absorbance readings at the lambda max. (at 621nm) peak. Figure 4 below shows a box plot analysis of the absorbance values based on absorption bands at 621 nm and at 760 nm for each of the three kinetic experiments. The values are derived from the absorbance readings from the three categories of the photodegradation kinetic experiments shown earlier in Fig. 3 . The box plot chart shows a comparison of the statistical distribution in the experimentally recorded numerical absorbance values (indication of a change in concentration) in terms of the spread/range, skew and variability in the three photodegradation kinetic experiments. It can be observed that in all three kinetic experiments, a range in the normalised absorbance values is recorded. However, the interquartile range (IQR) magnitudes are distinctively different when comparing the data sets obtained from the lambda max. readings at 760 nm. The [DNPz Dye + UV irrad.] has the least, while the [DNPz Dye + UV irrad. + MnO 2 ] has the greatest value based on the box plot analysis. The [DNPz Dye + MnO 2 ] experiment has an IQR value somewhere in between the other two experiments. The greatest spread, variability and skewness in the normalised absorbance data was recorded in the case of [DNPz. + UV irrad. + MnO 2 ] photodegradation experiment. This spread and variability are less in the case of the non-photocatalyzed [DNPz. + MnO 2 ] experiment, and even much less in the case of [DNPz. + UV irrad.]. Although a slight skew (relative to the median) is observed in the case [DNPz. + MnO 2 ] experiment, there is significant skew in the case of [DNPz. + UV irrad. + MnO 2 ] experiment. This means the rate of decrease in absorbance is higher in the latter case than in the former. This is attributed to the photocatalytic activity of MnO 2 on the degradation of DNPz molecules when coupled with UV irradiation. These results mirror other studies on UV-assisted and MnO 2 -mediated photodegradation of organic substances [ 14 , 15 ]. Analysis of Photodegradation Rates of DNPz Dye Figure 5 : Graphical kinetic profiles of DNPz (50 mg/L) degradation based on the [At/Ao] vs time data obtained by monitoring the degradation of DNPz on exposure to UV254 nm irradiation only = [DNPz.+UV irrad.], exposure to MnO 2 only = [DNPz.+MnO 2 ], and exposure to both UV254 nm irradiation and MnO 2 (1 ml of 5 mg/L) = [DNPz.+UV irrad. + MnO 2 ]: Fig. 5 a,b: The respective charts for the Linear and Log. transformed time scale kinetic profiles using absorbances at 621 nm and at 760 nm; Figs. 5 c,d: The respective charts for the Linear and Log. transformed time scale kinetic profiles using near-infra red absorption monitored over time at 1100 nm. It can be noted from the linear fits from the plotted kinetic profiles in Figs. 6a and 6c that the absorbance values (depicting concentrations) decrease over time in all three categories of experiments, but at varied degradation rates based on the slope/gradient values indicated therein. The [DNPz.+UV irrad.] The experiment has a marginal rate in comparison to the other two experiments. This means that although UV irradiation alone can cause decomposition of the DNPz dye, the degradation rate due to MnO 2 exposure is greater, as shown in the kinetic profile of the [DNPz.+MnO 2 ] experiment. Of all three kinetic experiments, [DNPz.+UV irrad.+MnO 2 ] shows the greatest degradation rate based on analysis of the gradients of the fitted kinetic profiles. This demonstrates the photocatalytic effect of MnO 2 on the degradation of DNPz molecules when exposed to UV 254 nm irradiation. Table 2 gives a summary of the average pseudo-first-order degradation rate constants obtained from the graphically fitted kinetic profiles in Fig. 5 a and 5 b. The lowest gradients are recorded in the case of [DNPz.+UV irrad.] as opposed to the other two experiments. The relative incremental ratios in the rate constants (based on the gradients) are represented in the last column. For the kinetic profiles monitored using the absorption bands at 621 nm and 760 nm, in the visible region, the average degradation rates of DNPz increase by ratios of 2.87–3.69 on exposure to MnO 2 with respect to exposure to UV irradiation only. Table 2 Comparison of average Pseudo 1st - Order Rate Constants ( K av .) from the kinetic experiments: [DNPz.+UV irrad.], [DNPz.+MnO 2 ], and [DNPz.+UV irrad.+MnO 2 ] Spectroscopic Absorption Bands for monitoring of degradation kinetics Average Pseudo 1st - Order Rate Contants ( K av .) based on gradients/slopes of the kinetic profiles. \(\:\raisebox{1ex}{$-d[DNPz.]$}\!\left/\:\!\raisebox{-1ex}{$dt$}\right.\) duration = (0–150 min) Relative Incremental Ratios [DNPz.+UV irrad.] ϒ [DNPz.+MnO 2 .] ρ [DNPz.+ MnO 2 +UV irrad.] ϕ ρ/ϒ ; ϕ/ρ ; ϕ/ ϒ Abs. band, (λ max .) at 621 nm 0.827 x 10 − 4 2.379 x 10 − 4 7.982 x 10 − 4 2.87 ; 3.35 ; 9.65 Abs. band at 760 nm 1.433 x 10 − 4 5.293 x 10 − 4 9.274 x 10 − 4 3.69 ; 1.75 ; 6.47 Abs. band at 1100 nm 7.982 x 10 − 4 9.281 x 10 − 4 11.211 x 10 − 4 1.16 ; 1.21 ; 1.40 Exposure of DNPz to UV irradiation in the presence of MnO 2, i.e. [DNPz.+MnO 2 +UV irrad.], has the highest values of gradients (or the rate constants) in all the experiments monitored by absorptions at 621 nm, 760 nm and 1100 nm. The incremental ratios in the rate (based on gradients) computed for the photocatalyzed degradation process [DNPz.+MnO 2 +UV irrad.], relative to the non-photocatalyzed degradation process [DNPz.+MnO 2 ], are 1.75 and 3.35 for experiments monitored at 621 nm and at 760 nm, respectively. The incremental ratios reflecting the catalytic effects of UV irradiation and MnO 2 on DNPz degradation are evident from the analysis of rates/gradients in the three kinetic experiments monitored using the NIR absorption band at 1100 nm recorded in the last row. Conclusions Kinetic and spectroscopic experiments that characterise the degradation of a dinaphthophenazine (DNPz) molecule, commercially available as Vat Blue 6 fluorescent textile dye, were studied by UV-Visible-NIR absorption spectroscopy under different conditions. The change in absorbance related to the DNPz molecule was monitored over time under exposure to UV irradiation only [DNPz.+UV irrad], MnO 2 only [DNPz.+MnO 2 ], and MnO 2 in the presence of UV irradiation [DNPz.+MnO 2 +UV irrad.]. Degradation was observed in all three conditions, but at different rates. A comparison of the kinetic profiles showed that degradation under exposure of the DNPz molecules to UV irradiation in the presence of MnO 2 gave the highest degradation rate, which was significantly higher than the exposure to UV irradiation alone. Exposure of DNPz to MnO 2 also showed marked degradation, albeit at lesser rates as opposed to the case where DNPz was exposed to both MnO 2 and UV irradiation. A comparison of the average first-order rate constants among the [DNPz.+MnO 2 ], and [DNPz.+MnO 2 +UV irrad.] Kinetic experiments revealed that MnO 2 has a significant photocatalytic effect on the degradation of DNPz dye. These scientific results add to the existing body of knowledge that could help provide a basis to support the development of a promising, cost-effective and green approach in chemical technology that can potentially be applied in the efficient remediation of dye-polluted discharge in textile industries. Declarations Author Contribution Kelvin. K. developed the original main manuscript text.Seth O. did the graphing, and statistical analysis.Josiah O. and John. A. reviewed the manuscript, performed data curation and technical editing. Acknowledgments We wish to acknowledge funding from the German Deutsche Gesellschaft fuer Internationale Zusammenarbeit (GIZ) GmbH, registered in Bonn, Germany, in the form of equipment and IT support that enabled the establishment of the Optical Spectroscopy laboratory at Egerton University, Chemistry Department, under grant no. CIM No. 50097076 under the Program for Migration and Development (PMD) initiative in Kenya. 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J Water Process Eng 66. https://doi.org/10.1016/j.jwpe.2024.106048 . :(September)106048 Additional Declarations No competing interests reported. Supplementary Files graphicalabstract.jpg Graphical abstract Cite Share Download PDF Status: Published Journal Publication published 02 Apr, 2026 Read the published version in Reaction Kinetics, Mechanisms and Catalysis → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8658954","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":583269220,"identity":"1b7d50a1-c5fa-47ea-98fb-9c3f77db6566","order_by":0,"name":"Kelvin Kimaru","email":"","orcid":"","institution":"Egerton University","correspondingAuthor":false,"prefix":"","firstName":"Kelvin","middleName":"","lastName":"Kimaru","suffix":""},{"id":583269224,"identity":"c963332a-f6b7-470e-acf9-b03d214e249f","order_by":1,"name":"Seth Otieno Osumba","email":"","orcid":"","institution":"Egerton 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Adongo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYBACxgYGAxAthyzITJQWYzDvADFagACsJbGBaC3M7Yc3Pi74ZZPez7/42OcPFXcY+NsPMBt8wOewnrRi45l9abkzZzxLnnHgzDMGiTMJzIkz8Polx0yat+dw7oYbZ4wZDrYdZmC4wcB8mAeflv43YC3p9jfOfwZrkQdp+YNPywygLTw/DicY8Pcwg7UYALUk4/M+44xnxca8DWmGM26wGTOcOXOYx/BMYrNhDx4thv3JGx/z/LGR5+8//JihouKwnNzxw4clfuDT0gCyqg1ISCSABXjA0YsPyINJkG/5D+BVOApGwSgYBSMYAAC5QVJDgWu2hQAAAABJRU5ErkJggg==","orcid":"","institution":"Egerton University","correspondingAuthor":true,"prefix":"","firstName":"John","middleName":"Onyango","lastName":"Adongo","suffix":""}],"badges":[],"createdAt":"2026-01-21 11:33:01","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8658954/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8658954/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11144-026-03095-z","type":"published","date":"2026-04-02T15:58:22+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":103302002,"identity":"c03d2ec2-0d75-432f-b91d-2f3ddcbd212f","added_by":"auto","created_at":"2026-02-24 08:22:04","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":235356,"visible":true,"origin":"","legend":"\u003cp\u003e(a) UV-Vis-Near-IR absorption spectra of DNPz and MnO\u003csub\u003e2\u003c/sub\u003e and (b) Corresponding 1\u003csup\u003est\u003c/sup\u003e– Order derivative spectra \u0026nbsp;\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/025c3c4e5fa90c6ada43721d.jpg"},{"id":103302003,"identity":"8b870a21-2c13-430d-9b88-703aa7db9abd","added_by":"auto","created_at":"2026-02-24 08:22:04","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":208509,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Vis-Near-IR Time-dependent absorption spectra characterising UV-Assisted photodegradation of DNPz molecule\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/4683fcbe10b878f6d8356f4c.jpg"},{"id":103506050,"identity":"ef722ea7-b772-4e87-9a71-9a9d0d84e06c","added_by":"auto","created_at":"2026-02-26 13:33:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":262160,"visible":true,"origin":"","legend":"\u003cp\u003eScans obtained from the kinetic experiments: [DNPz.+UV irrad.] (in Fig. 3a,b), [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e] (in Fig 3c,d), and [DNPz.+UV irrad. + MnO\u003csub\u003e2\u003c/sub\u003e] (in Fig 3e,f)\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/cbbdacbebe7b0cf39bbe8fab.jpg"},{"id":103505870,"identity":"9fd5b8e0-7dbe-404b-a219-dbfbe23924ee","added_by":"auto","created_at":"2026-02-26 13:33:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5713,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version\u003c/p\u003e","description":"","filename":"placeholderimage.png","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/b3392ae31d986aa180be271c.png"},{"id":103301997,"identity":"e9aba507-800f-46f6-aa74-60799992d142","added_by":"auto","created_at":"2026-02-24 08:22:04","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":125429,"visible":true,"origin":"","legend":"\u003cp\u003eBox plot chart for the normalised absorbance values in [DNPz.+UV irrad. only], [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e only], and [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.] kinetic experiments\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/90130a72f35a79968621a46c.jpg"},{"id":103301999,"identity":"d005021a-6170-48bf-8f2b-7985c3ee00b7","added_by":"auto","created_at":"2026-02-24 08:22:04","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":246892,"visible":true,"origin":"","legend":"\u003cp\u003eKinetic profiles for DNPz degradation using absorbances at 621 nm and 760 nm in Fig.6(a) and 6(b); and in the NIR range at 1100 nm in Fig. 6(c) and 6(d)\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/2a01395b1e312f49af509bc0.jpg"},{"id":106344051,"identity":"39db7ccb-aef1-4bdc-a3e9-6cb5793bd4d3","added_by":"auto","created_at":"2026-04-07 16:12:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1830552,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/52772543-8885-47a0-98fb-698c2de290f5.pdf"},{"id":103302000,"identity":"0c329653-7031-4c33-8ead-869ef497c8f7","added_by":"auto","created_at":"2026-02-24 08:22:04","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":200522,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"graphicalabstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8658954/v1/f08196da50a4aac12eeacc12.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Kinetics of UV-Assisted and MnO2 Photocatalysed Degradation of Dinaphthophenazine","fulltext":[{"header":"Article Highlights","content":"\u003cul\u003e\n \u003cli\u003eExposure of dinaphthophenazine textile dye to UV irradiation causes its photodegradation based on absorption measurements.\u003c/li\u003e\n \u003cli\u003eManganese (IV) oxide can degrade dinaphthophenazine dye at a higher rate than UV exposure.\u003c/li\u003e\n \u003cli\u003eThe degradation rate of dinaphthophenazine is significantly enhanced upon exposure to UV irradiation in the presence of MnO\u003csub\u003e2\u003c/sub\u003e. This demonstrates its photocatalytic effects.\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Introduction","content":"\u003cp\u003eCatalytic photo-oxidation is one of the most effective strategies, which could completely convert organic pollutants into harmless products like carbon dioxide and water. Currently, there are a number of metal oxides known that play roles in photocatalytic degradation strategies and technologies that exploit oxidation mechanisms to achieve promising degradation rates for organic pollutant materials [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e]. In recent years, a number of researchers have shown that manganese oxides and their composites can function as effective adsorbents and catalysts for remediating organic pollutants [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDinaphthophenazine (DNPz) is a derivative of phenazine, a dibenzoannulated pyrazine, a parent substance in many dyestuffs. The DNPz molecule constitutes a class of artificial water-soluble organic compounds commonly applied in textile dying. The DNPz synthetic dyes are derived from aromatic compounds containing amine functional groups as the precursor compounds. They are part larger class of synthetic Vat dyes, the majority of which are poly-condensed aromatic carbonyl compounds, and as such, they bear a close resemblance to anthraquinone dyestuffs \u003csup\u003e8,9\u003c/sup\u003e. When present in industrial textile wastewaters as residues, they can accumulate as environmentally hazardous pollutants [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e]. Despite their significant economic advantages in the textile industry, some of their synthetic precursors are associated with potentially adverse health risks to humans, such as skin cancers, lung cancers, allergies, neurocognitive effects and formation of haemoglobin adduct(s), among other deleterious health effects which have been linked to medium- or long- term exposures or ingestion [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, a derivative of DNPz textile organic dyestuff compound, with the trade name of Vat blue 6, was subjected to photodegradation experiments in the laboratory. Three experiments involving exposure of DNPz to UV-irradiation only [DNPz.+ UV only], exposure to MnO\u003csub\u003e2\u003c/sub\u003e [DNPz.+ MnO\u003csub\u003e2\u003c/sub\u003e only], and exposure to MnO\u003csub\u003e2\u003c/sub\u003e in presence of UV-irradiation [DNPz.+ MnO\u003csub\u003e2\u003c/sub\u003e + UV irradiation.] were set up to investigate the photodegradation of the NPz molecule. Time-dependent wavelength scan absorption spectra were acquired during the photodegradation reactions using UV-Visible spectroscopy. The absorption spectra were plotted in graphs and charts as a function of time to characterise and evaluate the rates of decrease in NPz concentrations resulting from the exposure conditions.\u003c/p\u003e \u003cp\u003eIn all three kinetic experiments [DNPz.+ UV irrad], [DNPz.+ MnO\u003csub\u003e2\u003c/sub\u003e only], [(DNPz) + MnO\u003csub\u003e2\u003c/sub\u003e + UV irradiation.], a gradual decrease in the absorption spectra over the same time interval, characterising the degradation reactions, was observed. Varying average first-order photodegradation rate constants were recorded. Kinetic analyses of the spectroscopic data showed that exposure of DNPz to MnO\u003csub\u003e2\u003c/sub\u003e only and MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV irradiation gave significantly higher average first-order photodegradation rate constants as opposed to exposure to UV-irradiation only.\u003c/p\u003e "},{"header":"Experimental","content":"\u003cp\u003e \u003cb\u003eReagents\u003c/b\u003e: Analytical grade (% purity \u0026gt; 99%) versions of manganese (VI) oxide (acidified), 70% acetone and deionised water (DI) were acquired from Kobian distributors limited. A dinaphthophenazine (DNPz) dye [Trade Name: Blue K fluorescent dye, Vat-Blue 6 (Mwt. = 511.31 g/mol) IUPAC Name: 7,16-dichloro-6,15-dihydrodinaphtho[2,3-a:2',3'-h]phenazine-5,9,14,18-tetraone Mol. Formula: C\u003csub\u003e28\u003c/sub\u003eH\u003csub\u003e12\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e] was purchased from Gala Textile Ltd, Nairobi, Kenya.\u003c/p\u003e\u003cp\u003e \u003cstrong\u003eInstrumentation\u003c/strong\u003e \u003c/p\u003e\u003cp\u003eShimadzu model (AUY 120) analytical balance was used for weight measurements. Spectral data acquisition was done with a double-beam UV-Visible-Near IR spectrometer (UV-VIS K9000 model). Ultraviolet irradiation experiments were conducted using with UV-lamp (UVI-TEC model). A Texas Instruments LED digital watch was used as the timer for the spectra acquisition degradation experiments.\u003c/p\u003e\u003cp\u003e \u003cstrong\u003eMethod\u003c/strong\u003e \u003c/p\u003e\u003cp\u003eIn this study, the degradation experiments were optimised and conducted in a photocell chamber. To investigate the effect of UV radiation on DNPz. degradation, 3.5 mL of 50 mg/L of DNPz dye in 70% acetone was exposed directly to UV light of 48 W/cm\u003csup\u003e2\u003c/sup\u003e, 254 nm in the kinetic experiment labelled [DNPz. dye + UV irrad. only] and absorption spectra acquired at time intervals of 0 min., 10 min., 20 min., 30 min., 50 min., 1hr.10 min, 1hr.30 min., 2hr. 30min. To establish the effect of MnO\u003csub\u003e2\u003c/sub\u003e on DNPz dye degradation, 1 mL drop of 5 mg/L of MnO\u003csub\u003e2\u003c/sub\u003e in DI water was added to 2.5 mL of 50 mg/L of DNPz dye in 70% acetone in the kinetic experiment [DNPz. dye + MnO\u003csub\u003e2\u003c/sub\u003e only] in the dark. The degradation of the dye was monitored using periodic wavelength scan UV-Vis-NIR absorption spectra acquired at similar intervals as in the case of UV irradiation only. To further investigate the photocatalytic effect of MnO\u003csub\u003e2\u003c/sub\u003e on the degradation of DNPz dye, the kinetic experiment [DNPz. dye + MnO\u003csub\u003e2\u003c/sub\u003e + UV irrad.] was a setup and spectra acquired at similar time intervals for comparison reasons. The kinetic profiles for the three experiments were graphed in multicurve plots, box charts, OriginPro®v.9.0.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eUV-VIS-Near-IR Characterisation of DNPz Dye and its Photodegradation\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea below shows the UV-Vis-NIR absorption spectra of the dinaphthophenazine (DNPz) textile dye (in Orange and blue). The wavelength scans span the range 1100 nm to 250 nm. The spectrum in red was obtained from a freshly prepared sample of manganese(IV) oxide (MnO\u003csub\u003e2\u003c/sub\u003e) in aqueous solution. These plots act as important spectral references for monitoring the changes in concentration of the absorbing species (or chromophores) over time to determine the kinetic profiles of degradation, reaction rates, and to characterise catalytic activities [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe MnO\u003csub\u003e2\u003c/sub\u003e spectrum in red does not show any absorption that coincides with the broad absorption band recorded for DNPz (in Orange) and DNPz+MnO\u003csub\u003e2\u003c/sub\u003e (in blue) within the visible and near IR regions. It can be observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea that the textile organic dye molecule NPz exhibits a very broad absorption across the ultraviolet, visible and near-IR ranges with a maximum absorption in the visible range at 621 nm. The absorption of DNPz dye is also characterised by a shoulder peak at 760 nm. The extensive conjugation in the DNPz contributes to the broad absorption observed in its UV-Vis-NIR spectra. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb shows the first-order derivative spectra from the respective spectra in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. It confirms further that the derivatives are at zero at 760 nm and at 621 nm for the corresponding peaks identified in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. It can also be noted from Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea that there is some absorption in the near IR region 1050\u0026ndash;1100 nm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depicts UV-Vis-NIR wavelength scan absorption spectra acquired over time. They characterise UV-Assisted photodegradation of the DNPz molecule based on the observed decrease in absorbance over time upon exposure of DNPz to UV 254 nm irradiation. The inset figure shows all the spectra acquired during the [DNPz.+UV irrad.] kinetic experiment within the near-IR region highlighted more clearly. The general decrease in absorption (or concentration) over time, evidently observed in the spectra, characterises UV-assisted photodegradation of DNPz molecules. A similar trend of decreasing absorbance over time is observed at the Lamba max. of 621 nm and the shoulder peak at 760 nm.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eKinetics of DNPz Degradation and Photocatalytic Effect of MnO\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the spectra derived from three kinetic experimental setups: [DNPz.+UV irrad.] (in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea,b), [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e] (in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec,d), and [NPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e] (in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee,f) that we conducted to evaluate and characterise the photodegradation rates of the NPz dye under different conditions. In all three experiments, the initial concentration of NPz was held at 0.1M while studying the effect of UV irradiation, exposure to MnO\u003csub\u003e2\u003c/sub\u003e and exposure to MnO\u003csub\u003e2\u003c/sub\u003e coupled with UV irradiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe absorption bands within the visible region, λ max. value at 621 nm and the shoulder peak at 760 nm, were used to spectroscopically characterise and compare the degradation rates based on the changes in absorbance values, d \u003csub\u003eAbs\u003c/sub\u003e. (reflecting changes in concentration) among the three categories of experiments conducted within similar time intervals (0 min. to 2hr. 30 min.). In all three experiments, a decrease in absorbance was observed, but at varying rates. The difference in absorbance values recorded just at the start of the experiment (Abs. t\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e= 0 min.) and at the end of the experiment (Abs. t\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e = 2hr. 30min.) was used to compute the overall change in absorbance (d \u003csub\u003eAbs.),\u003c/sub\u003e for each experiment as shown in all the charts in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. All the d\u003csub\u003eAbs\u003c/sub\u003e. values are summarised in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The calculated ratios, b/a and c/a, in the last column indicate the incremental effects of MnO\u003csub\u003e2\u003c/sub\u003e and UV irradiation (in the presence of MnO\u003csub\u003e2\u003c/sub\u003e) on the photodegradation rates of DNPz dye..\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of change in absorbance (d\u003csub\u003eAbs\u003c/sub\u003e.) values from the kinetic experiments: [DNPz.+UV irrad.], [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and [DNPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSpectroscopic Absorption Bands in the Visible region\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eChange in Abs. (d Abs.)\u003c/p\u003e \u003cp\u003e(Initial Abs. \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e = 0 min \u0026ndash; Final Abs. \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e = 2hr.30min.)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIncremental ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[DNPz.+UV irrad.]\u003c/p\u003e \u003cp\u003ea\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e.]\u003c/p\u003e \u003cp\u003eb\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e[DNPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e]\u003c/p\u003e \u003cp\u003ec\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eb/a ; c/a\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbs. band, (λ \u003csub\u003emax\u003c/sub\u003e.) at 621 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.0 x 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.8 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.8 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.11 ; 5.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbs. band at\u003c/p\u003e \u003cp\u003e760 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.2 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.6 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.0 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.33 ; 1.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIt can be noted from Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e that the greatest change in concentration (based on absorbance data) was recorded from the [DNPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e], where both UV irradiation and MnO\u003csub\u003e2\u003c/sub\u003e were used to cause degradation. The least change in concentration for the same period of time was observed in the [DNPz.+UV irrad.] experiment, where only UV irradiation was used to degrade DNPz molecules. It was also observed that MnO\u003csub\u003e2\u003c/sub\u003e caused some degradation of the DNPz molecules, even without UV irradiation in the [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e] kinetic experiment. The incremental ratios are calculated with respect to the d\u003csub\u003eAbs\u003c/sub\u003e. values of [DNPz.+UV irrad.] The experiment revealed that MnO\u003csub\u003e2\u003c/sub\u003e increased the d\u003csub\u003eAbs\u003c/sub\u003e. value by a factor of about 3.11, while MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV irradiation increases it by about 5.33 based on the absorbance readings at the lambda max. (at 621nm) peak.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e below shows a box plot analysis of the absorbance values based on absorption bands at 621 nm and at 760 nm for each of the three kinetic experiments. The values are derived from the absorbance readings from the three categories of the photodegradation kinetic experiments shown earlier in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The box plot chart shows a comparison of the statistical distribution in the experimentally recorded numerical absorbance values (indication of a change in concentration) in terms of the spread/range, skew and variability in the three photodegradation kinetic experiments. It can be observed that in all three kinetic experiments, a range in the normalised absorbance values is recorded. However, the interquartile range (IQR) magnitudes are distinctively different when comparing the data sets obtained from the lambda max. readings at 760 nm. The [DNPz Dye\u0026thinsp;+\u0026thinsp;UV irrad.] has the least, while the [DNPz Dye\u0026thinsp;+\u0026thinsp;UV irrad. + MnO\u003csub\u003e2\u003c/sub\u003e] has the greatest value based on the box plot analysis. The [DNPz Dye\u0026thinsp;+\u0026thinsp;MnO\u003csub\u003e2\u003c/sub\u003e] experiment has an IQR value somewhere in between the other two experiments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe greatest spread, variability and skewness in the normalised absorbance data was recorded in the case of [DNPz. + UV irrad. + MnO\u003csub\u003e2\u003c/sub\u003e] photodegradation experiment. This spread and variability are less in the case of the non-photocatalyzed [DNPz. + MnO\u003csub\u003e2\u003c/sub\u003e] experiment, and even much less in the case of [DNPz. + UV irrad.]. Although a slight skew (relative to the median) is observed in the case [DNPz. + MnO\u003csub\u003e2\u003c/sub\u003e] experiment, there is significant skew in the case of [DNPz. + UV irrad. + MnO\u003csub\u003e2\u003c/sub\u003e] experiment. This means the rate of decrease in absorbance is higher in the latter case than in the former. This is attributed to the photocatalytic activity of MnO\u003csub\u003e2\u003c/sub\u003e on the degradation of DNPz molecules when coupled with UV irradiation. These results mirror other studies on UV-assisted and MnO\u003csub\u003e2\u003c/sub\u003e-mediated photodegradation of organic substances [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003eAnalysis of Photodegradation Rates of DNPz Dye\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e: Graphical kinetic profiles of DNPz (50 mg/L) degradation based on the [At/Ao] vs time data obtained by monitoring the degradation of DNPz on exposure to UV254 nm irradiation only = [DNPz.+UV irrad.], exposure to MnO\u003csub\u003e2\u003c/sub\u003e only = [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and exposure to both UV254 nm irradiation and MnO\u003csub\u003e2\u003c/sub\u003e (1 ml of 5 mg/L) = [DNPz.+UV irrad. + MnO\u003csub\u003e2\u003c/sub\u003e]: Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea,b: The respective charts for the Linear and Log. transformed time scale kinetic profiles using absorbances at 621 nm and at 760 nm; Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d: The respective charts for the Linear and Log. transformed time scale kinetic profiles using near-infra red absorption monitored over time at 1100 nm.\u003c/p\u003e \u003cp\u003eIt can be noted from the linear fits from the plotted kinetic profiles in Figs.\u0026nbsp;6a and 6c that the absorbance values (depicting concentrations) decrease over time in all three categories of experiments, but at varied degradation rates based on the slope/gradient values indicated therein. The [DNPz.+UV irrad.] The experiment has a marginal rate in comparison to the other two experiments. This means that although UV irradiation alone can cause decomposition of the DNPz dye, the degradation rate due to MnO\u003csub\u003e2\u003c/sub\u003e exposure is greater, as shown in the kinetic profile of the [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e] experiment. Of all three kinetic experiments, [DNPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e] shows the greatest degradation rate based on analysis of the gradients of the fitted kinetic profiles. This demonstrates the photocatalytic effect of MnO\u003csub\u003e2\u003c/sub\u003e on the degradation of DNPz molecules when exposed to UV\u003csub\u003e254 nm\u003c/sub\u003e irradiation.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e gives a summary of the average pseudo-first-order degradation rate constants obtained from the graphically fitted kinetic profiles in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. The lowest gradients are recorded in the case of [DNPz.+UV irrad.] as opposed to the other two experiments. The relative incremental ratios in the rate constants (based on the gradients) are represented in the last column. For the kinetic profiles monitored using the absorption bands at 621 nm and 760 nm, in the visible region, the average degradation rates of DNPz increase by ratios of 2.87\u0026ndash;3.69 on exposure to MnO\u003csub\u003e2\u003c/sub\u003e with respect to exposure to UV irradiation only.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of average Pseudo 1st - Order Rate Constants (\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eav\u003c/em\u003e\u003c/sub\u003e.) from the kinetic experiments: [DNPz.+UV irrad.], [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and [DNPz.+UV irrad.+MnO\u003csub\u003e2\u003c/sub\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSpectroscopic Absorption Bands for monitoring of degradation kinetics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eAverage Pseudo 1st - Order Rate Contants (\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eav\u003c/em\u003e\u003c/sub\u003e.) based on gradients/slopes of the kinetic profiles.\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\raisebox{1ex}{$-d[DNPz.]$}\\!\\left/\\:\\!\\raisebox{-1ex}{$dt$}\\right.\\)\u003c/span\u003e\u003c/span\u003e duration = (0\u0026ndash;150 min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRelative Incremental Ratios\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[DNPz.+UV irrad.]\u003cem\u003eϒ\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e.]\u003cem\u003eρ\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e[DNPz.+ MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.]\u003cem\u003eϕ\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eρ/ϒ\u003c/em\u003e ; \u003cem\u003eϕ/ρ ; ϕ/ ϒ\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbs. band, (λ \u003csub\u003emax\u003c/sub\u003e.)\u003c/p\u003e \u003cp\u003eat 621 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.827 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.379 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.982 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.87 ; 3.35 ; 9.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbs. band at 760 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.433 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.293 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.274 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.69 ; 1.75 ; 6.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbs. band at 1100 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.982 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.281 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.211 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.16 ; 1.21 ; 1.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eExposure of DNPz to UV irradiation in the presence of MnO\u003csub\u003e2,\u003c/sub\u003e i.e. [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.], has the highest values of gradients (or the rate constants) in all the experiments monitored by absorptions at 621 nm, 760 nm and 1100 nm. The incremental ratios in the rate (based on gradients) computed for the photocatalyzed degradation process [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.], relative to the non-photocatalyzed degradation process [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], are 1.75 and 3.35 for experiments monitored at 621 nm and at 760 nm, respectively. The incremental ratios reflecting the catalytic effects of UV irradiation and MnO\u003csub\u003e2\u003c/sub\u003e on DNPz degradation are evident from the analysis of rates/gradients in the three kinetic experiments monitored using the NIR absorption band at 1100 nm recorded in the last row.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eKinetic and spectroscopic experiments that characterise the degradation of a dinaphthophenazine (DNPz) molecule, commercially available as Vat Blue 6 fluorescent textile dye, were studied by UV-Visible-NIR absorption spectroscopy under different conditions. The change in absorbance related to the DNPz molecule was monitored over time under exposure to UV irradiation only [DNPz.+UV irrad], MnO\u003csub\u003e2\u003c/sub\u003e only [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV irradiation [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.]. Degradation was observed in all three conditions, but at different rates. A comparison of the kinetic profiles showed that degradation under exposure of the DNPz molecules to UV irradiation in the presence of MnO\u003csub\u003e2\u003c/sub\u003e gave the highest degradation rate, which was significantly higher than the exposure to UV irradiation alone. Exposure of DNPz to MnO\u003csub\u003e2\u003c/sub\u003e also showed marked degradation, albeit at lesser rates as opposed to the case where DNPz was exposed to both MnO\u003csub\u003e2\u003c/sub\u003e and UV irradiation. A comparison of the average first-order rate constants among the [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e+UV irrad.] Kinetic experiments revealed that MnO\u003csub\u003e2\u003c/sub\u003e has a significant photocatalytic effect on the degradation of DNPz dye. These scientific results add to the existing body of knowledge that could help provide a basis to support the development of a promising, cost-effective and green approach in chemical technology that can potentially be applied in the efficient remediation of dye-polluted discharge in textile industries.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eKelvin. K. developed the original main manuscript text.Seth O. did the graphing, and statistical analysis.Josiah O. and John. A. reviewed the manuscript, performed data curation and technical editing.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eWe wish to acknowledge funding from the German Deutsche Gesellschaft fuer Internationale Zusammenarbeit (GIZ) GmbH, registered in Bonn, Germany, in the form of equipment and IT support that enabled the establishment of the Optical Spectroscopy laboratory at Egerton University, Chemistry Department, under grant no. CIM No. 50097076 under the Program for Migration and Development (PMD) initiative in Kenya.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting Interests\u003c/strong\u003e \u003cp\u003eAuthors declare no conflict of interests or competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data supporting the findings of this study are available within the paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSun G, Gao Y, Luo X, Lian L, He J, Xie S, Su J, Liu T, Xu L (2025) Recent Advances in Formaldehyde Catalytic Oxidation Catalysts. 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J Water Process Eng 66. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jwpe.2024.106048\u003c/span\u003e\u003cspan address=\"10.1016/j.jwpe.2024.106048\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. :(September)106048\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Photodegradation, UV-irradiation, Dinaphthophenazine, Manganese (IV)oxide, Photocatalytic effect","lastPublishedDoi":"10.21203/rs.3.rs-8658954/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8658954/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe treatment of the dye-contaminated wastewater using ultraviolet (UV)-induced photodegradation, metal oxides and photocatalysts continues to be investigated by chemists towards improving dye-pollutant remediation technologies for environmental protection.\u0026nbsp; In this study, a Dinaphthophenazine (DNPz.) textile dye was subjected to degradation experiments to characterise its degradation rates and highlight the photocatalytic degradation effect of manganese (IV)oxide (MnO\u003csub\u003e2\u003c/sub\u003e) by comparing the kinetics of UV-induced degradation against MnO\u003csub\u003e2\u003c/sub\u003e – catalyzed photodegradation. Kinetic experiments were conducted by acquiring time-dependent wavelength scan absorption spectra at intervals using double-beam UV-Vis-NIR spectroscopy and a photo-cell setup. A multicurve kinetic profile plot analysis of the three experiments: exposure of DNPz to UV irradiation [DNPz.+UV irrad.], exposure of DNPz to MnO\u003csub\u003e2\u003c/sub\u003e only [DNPz.+MnO\u003csub\u003e2\u003c/sub\u003e], and the exposure of DNPz to a similar dose of MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV 254 nm irradiation revealed a decrease in absorbance related to the DNPz molecule over time, indicating degradation of DNPz molecules under acidic conditions, pH 5.0 and at room temperature. A comparative analysis of the pseudo-1\u003csup\u003est\u003c/sup\u003e-Order degradation rates shows that exposure of DNPz to MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV irradiation gave the most significant average rate constant, which is about 9.65 times faster than in the case of the UV-assisted photodegradation based on kinetics monitored using DNPz’s Lambda max. absorptions at 621 nm. This is due to the photocatalytic effect of MnO\u003csub\u003e2\u003c/sub\u003e. The exposure to MnO\u003csub\u003e2\u003c/sub\u003e showed a marked increase in DNPz degradation rate that was about 3.31 times that of the average photodegradation rate recorded by exposure to UV 254 nm irradiation only. These results show that MnO\u003csub\u003e2\u003c/sub\u003e in the presence of UV 254 nm can significantly enhance the degradation of the DNPz textile dye.\u003c/p\u003e","manuscriptTitle":"Kinetics of UV-Assisted and MnO2 Photocatalysed Degradation of Dinaphthophenazine","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-24 08:21:58","doi":"10.21203/rs.3.rs-8658954/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1a7db017-e69b-45ac-a55e-a0f564c0665c","owner":[],"postedDate":"February 24th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-07T16:07:51+00:00","versionOfRecord":{"articleIdentity":"rs-8658954","link":"https://doi.org/10.1007/s11144-026-03095-z","journal":{"identity":"reaction-kinetics-mechanisms-and-catalysis","isVorOnly":false,"title":"Reaction Kinetics, Mechanisms and Catalysis"},"publishedOn":"2026-04-02 15:58:22","publishedOnDateReadable":"April 2nd, 2026"},"versionCreatedAt":"2026-02-24 08:21:58","video":"","vorDoi":"10.1007/s11144-026-03095-z","vorDoiUrl":"https://doi.org/10.1007/s11144-026-03095-z","workflowStages":[]},"version":"v1","identity":"rs-8658954","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8658954","identity":"rs-8658954","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}