Photolytic degradation of nitrofurantoine

Farmaceutici prisutni u okolišu mogu se razgraditi na različite načine. Za farmaceutike koji nisu podložni biorazgradnji i hidrolizi, direktna i indirektna fotoliza djelovanjem Sunčeve svjetlosti najznačajniji je put abiotičke razgradnje u površinskim vodama. Cilj ovoga rada bio je proučiti direktnu i indirektnu fotolitičku razgradnju farmaceutika nitrofurantoina. Otopine nitrofurantoina pripremljene su u MilliQ vodi s pH-vrijednostima 4, 6, 8 i 10, izvorskoj vodi, sintetskoj otpadnoj vodi te otopinama klorida, sulfata, nitrata, fosfata i huminskih kiselina. Pripremljene otopine izlagane su umjetnom Sunčevom zračenju te je tijek fotolitičke razgradnje praćen tekućinskom kromatografijom visoke djelotvornosti vezanoj detektorom s nizom dioda (HPLC-DAD). Rezultati istraživanja pokazali su da fotolitička razgradnja nitrofurantoina ovisi o pH-vrijednosti, povećanjem pH-vrijednosti vode, brzina se smanjuje. Također, rezultati pokazuju da sastav matice uzorka vode utječe na brzinu fotolitičke razgradnje NFT-a te je ispitan utjecaj pojedinih sastojaka matice (Cl-, huminske kiseline, NO3-, SO42-, PO43-). Najznačajniji utjecaj u vidu smanjenja brzine razgradnje uočen je u prisutnosti huminskih kiselina i fosfata. Dobiveni rezultati u ovome radu pridonijet će boljem razumijevanju ponašanja antibiotika nitrofurantoina u vodama u okolišu te mogućem utjecaju na ljudsko zdravlje i okoliš.The pharmaceuticals present int he environment may be degraded in difrent ways. For pharmaceuticals that are not subject to biodegradation and hydrolysis, direct and indirect photolysis by sunlight is the most important mechanism of degradation in surface waters. The aim of this work was to study the direct and indirect photolytic degradation of the anibiotic nitrofurantoin. Nitrofurantoin solutions prepared in MilliQ water with a pH value of 4,6,8 and 10; spring water, synthetic waste water and solutions of chloride, sulfate, nitrate, phosphate and humanic acid were prepared and exposed to artifical solar radiation. The rate of photolytic degradation was monitored by high performance liquid chromatography with diode array detection (HPLC-DAD). The results showed that the photolytic degradation of nitrofurantoin depends on pH; the degradation is slower in the solutions with higher pH values. Also, degradation rate depends on matrix composition and therefore degradation the impact of individual ions (Cl-, humic acid, NO3-, SO42-, PO43-) were investigates. The most significat reduction in degradation rate was observed int he presence of humic acids and phosphate. The results of this study will contribute to a better understanding of the fate of nitrofurantoin in the environment and the possible impact on human health and the environment

Photolytic degradation of nitrofurantoine

Farmaceutici prisutni u okolišu mogu se razgraditi na različite načine. Za farmaceutike koji nisu podložni biorazgradnji i hidrolizi, direktna i indirektna fotoliza djelovanjem Sunčeve svjetlosti najznačajniji je put abiotičke razgradnje u površinskim vodama. Cilj ovoga rada bio je proučiti direktnu i indirektnu fotolitičku razgradnju farmaceutika nitrofurantoina. Otopine nitrofurantoina pripremljene su u MilliQ vodi s pH-vrijednostima 4, 6, 8 i 10, izvorskoj vodi, sintetskoj otpadnoj vodi te otopinama klorida, sulfata, nitrata, fosfata i huminskih kiselina. Pripremljene otopine izlagane su umjetnom Sunčevom zračenju te je tijek fotolitičke razgradnje praćen tekućinskom kromatografijom visoke djelotvornosti vezanoj detektorom s nizom dioda (HPLC-DAD). Rezultati istraživanja pokazali su da fotolitička razgradnja nitrofurantoina ovisi o pH-vrijednosti, povećanjem pH-vrijednosti vode, brzina se smanjuje. Također, rezultati pokazuju da sastav matice uzorka vode utječe na brzinu fotolitičke razgradnje NFT-a te je ispitan utjecaj pojedinih sastojaka matice (Cl-, huminske kiseline, NO3-, SO42-, PO43-). Najznačajniji utjecaj u vidu smanjenja brzine razgradnje uočen je u prisutnosti huminskih kiselina i fosfata. Dobiveni rezultati u ovome radu pridonijet će boljem razumijevanju ponašanja antibiotika nitrofurantoina u vodama u okolišu te mogućem utjecaju na ljudsko zdravlje i okoliš.The pharmaceuticals present int he environment may be degraded in difrent ways. For pharmaceuticals that are not subject to biodegradation and hydrolysis, direct and indirect photolysis by sunlight is the most important mechanism of degradation in surface waters. The aim of this work was to study the direct and indirect photolytic degradation of the anibiotic nitrofurantoin. Nitrofurantoin solutions prepared in MilliQ water with a pH value of 4,6,8 and 10; spring water, synthetic waste water and solutions of chloride, sulfate, nitrate, phosphate and humanic acid were prepared and exposed to artifical solar radiation. The rate of photolytic degradation was monitored by high performance liquid chromatography with diode array detection (HPLC-DAD). The results showed that the photolytic degradation of nitrofurantoin depends on pH; the degradation is slower in the solutions with higher pH values. Also, degradation rate depends on matrix composition and therefore degradation the impact of individual ions (Cl-, humic acid, NO3-, SO42-, PO43-) were investigates. The most significat reduction in degradation rate was observed int he presence of humic acids and phosphate. The results of this study will contribute to a better understanding of the fate of nitrofurantoin in the environment and the possible impact on human health and the environment

Chromatographic methods for the monitoring of photocatalytic degradation of hydroxychloroquine

U ovom radu razvijene su metode HPLC-DAD i HPLC-FLD za praćenje farmaceutika hidroksiklorokina u uzorcima vode. U okviru validacije razvijenih metoda ispitana je linearnost, osjetljivost i točnost, te su određene granice detekcije i kvantifikacije i radno područje metoda. Usporedbom izvedbenih značajki obje metode zaključeno je da je metoda HPLC-FLD prihvatljivija za analizu hidroksiklorokina jer omogućava određivanje nižih koncentracija ispitivanog farmaceutika. Obje razvijene metode primijenjene su za praćenje fotolitičke i fotokatalitičke razgradnje hidroksiklorokina. U drugom dijelu rada ispitana je fotolitička i fotokatalitička razgradnja hidroksiklorokina uz primjenu TiO2 kao fotokatalizatora u obliku tankog filma i suspenzije te različitih izvora zračenja: LED svjetiljka 365 nm i 405 nm, svjetiljka sa zračenjem sličnim Sunčevom i halogena svjetiljka. Rezultati fotolitičke i fotokatalitičke razgradnje hidroksiklorokina pokazali su da nije podložan fotolitičkoj razgradnji, a fotokatalitička razgradnja brža je uz fotokatlizator prisutan u obliku suspenzije. Kinetika fotokatalitičke razgradnje slijedi kinetiku prvog reda. Validiranom metodom HPLC-FLD uočeno je nastajanje četiri razgradna produkta tijekom fotokatalitičke razgradnje LED svjetiljkom 365 nm, dok se tijekom fotoktalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm javljaju tri razgradna produkta. Validiranom metodom HPLC-DAD uočeno je nastajanje dva razgradna produkta tijekom fotokatalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm, dok validiranom metodom uz osvjetljavanje LED svjetiljkom 365 nm nisu detektirani razgradni produkti.In this paper, HPLC-DAD and HPLC-FLD methods have been developed to monitor the hydroxylchloroquine pharmaceuticals in water samples. Within the validation of the methods developed, linearity, sensitivity and accuracy were examined, and the limits of detection and quantification and the working range of the method were determined. By comparing the performance characteristics of both methods, it was concluded that the HPLC-FLD method is more acceptable for the analysis of hydroxychloroquine because it allows the determination of lower concentrations of the investigated drug. Both methods were used to monitor photolytic and photocatalytic degradation of hydroxychloroquines. In the second part, photolytic and photocatalytic degradation of hydroxychloroquine was investigated using TiO2 as photocatalysts in the form of thin film and suspensions and various sources of radiation: LED lamps at wavelengths of 365 and 405 nm, solar - like lamp and halogen lamp. The results of photolytic and photocatalytic degradation of hydroxychloroquines have shown that they are not subject to photolytic degradation, and photocatalytic degradation is faster with the photocatalyst present in the form of suspension. Photocatalytic degradation kinetics follows the kinetics of the first order. Using the validated HPLC-FLD method, four degradation products were detected during photocatalytic degradation by a 365 nm LED lamp, whilst during photocatalytic degradation with 405 nm LED lamp, there were three degradation products. Using the validated HPLC-DAD method, two degradation products were detected during photocatalytic degradation by a 405 nm LED lamp, whilst during photocatalytic degradation with 365 nm LED lamp did not detect any degradant products

Photolytic degradation of nitrofurantoine

Farmaceutici prisutni u okolišu mogu se razgraditi na različite načine. Za farmaceutike koji nisu podložni biorazgradnji i hidrolizi, direktna i indirektna fotoliza djelovanjem Sunčeve svjetlosti najznačajniji je put abiotičke razgradnje u površinskim vodama. Cilj ovoga rada bio je proučiti direktnu i indirektnu fotolitičku razgradnju farmaceutika nitrofurantoina. Otopine nitrofurantoina pripremljene su u MilliQ vodi s pH-vrijednostima 4, 6, 8 i 10, izvorskoj vodi, sintetskoj otpadnoj vodi te otopinama klorida, sulfata, nitrata, fosfata i huminskih kiselina. Pripremljene otopine izlagane su umjetnom Sunčevom zračenju te je tijek fotolitičke razgradnje praćen tekućinskom kromatografijom visoke djelotvornosti vezanoj detektorom s nizom dioda (HPLC-DAD). Rezultati istraživanja pokazali su da fotolitička razgradnja nitrofurantoina ovisi o pH-vrijednosti, povećanjem pH-vrijednosti vode, brzina se smanjuje. Također, rezultati pokazuju da sastav matice uzorka vode utječe na brzinu fotolitičke razgradnje NFT-a te je ispitan utjecaj pojedinih sastojaka matice (Cl-, huminske kiseline, NO3-, SO42-, PO43-). Najznačajniji utjecaj u vidu smanjenja brzine razgradnje uočen je u prisutnosti huminskih kiselina i fosfata. Dobiveni rezultati u ovome radu pridonijet će boljem razumijevanju ponašanja antibiotika nitrofurantoina u vodama u okolišu te mogućem utjecaju na ljudsko zdravlje i okoliš.The pharmaceuticals present int he environment may be degraded in difrent ways. For pharmaceuticals that are not subject to biodegradation and hydrolysis, direct and indirect photolysis by sunlight is the most important mechanism of degradation in surface waters. The aim of this work was to study the direct and indirect photolytic degradation of the anibiotic nitrofurantoin. Nitrofurantoin solutions prepared in MilliQ water with a pH value of 4,6,8 and 10; spring water, synthetic waste water and solutions of chloride, sulfate, nitrate, phosphate and humanic acid were prepared and exposed to artifical solar radiation. The rate of photolytic degradation was monitored by high performance liquid chromatography with diode array detection (HPLC-DAD). The results showed that the photolytic degradation of nitrofurantoin depends on pH; the degradation is slower in the solutions with higher pH values. Also, degradation rate depends on matrix composition and therefore degradation the impact of individual ions (Cl-, humic acid, NO3-, SO42-, PO43-) were investigates. The most significat reduction in degradation rate was observed int he presence of humic acids and phosphate. The results of this study will contribute to a better understanding of the fate of nitrofurantoin in the environment and the possible impact on human health and the environment

Chromatographic methods for the monitoring of photocatalytic degradation of hydroxychloroquine

U ovom radu razvijene su metode HPLC-DAD i HPLC-FLD za praćenje farmaceutika hidroksiklorokina u uzorcima vode. U okviru validacije razvijenih metoda ispitana je linearnost, osjetljivost i točnost, te su određene granice detekcije i kvantifikacije i radno područje metoda. Usporedbom izvedbenih značajki obje metode zaključeno je da je metoda HPLC-FLD prihvatljivija za analizu hidroksiklorokina jer omogućava određivanje nižih koncentracija ispitivanog farmaceutika. Obje razvijene metode primijenjene su za praćenje fotolitičke i fotokatalitičke razgradnje hidroksiklorokina. U drugom dijelu rada ispitana je fotolitička i fotokatalitička razgradnja hidroksiklorokina uz primjenu TiO2 kao fotokatalizatora u obliku tankog filma i suspenzije te različitih izvora zračenja: LED svjetiljka 365 nm i 405 nm, svjetiljka sa zračenjem sličnim Sunčevom i halogena svjetiljka. Rezultati fotolitičke i fotokatalitičke razgradnje hidroksiklorokina pokazali su da nije podložan fotolitičkoj razgradnji, a fotokatalitička razgradnja brža je uz fotokatlizator prisutan u obliku suspenzije. Kinetika fotokatalitičke razgradnje slijedi kinetiku prvog reda. Validiranom metodom HPLC-FLD uočeno je nastajanje četiri razgradna produkta tijekom fotokatalitičke razgradnje LED svjetiljkom 365 nm, dok se tijekom fotoktalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm javljaju tri razgradna produkta. Validiranom metodom HPLC-DAD uočeno je nastajanje dva razgradna produkta tijekom fotokatalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm, dok validiranom metodom uz osvjetljavanje LED svjetiljkom 365 nm nisu detektirani razgradni produkti.In this paper, HPLC-DAD and HPLC-FLD methods have been developed to monitor the hydroxylchloroquine pharmaceuticals in water samples. Within the validation of the methods developed, linearity, sensitivity and accuracy were examined, and the limits of detection and quantification and the working range of the method were determined. By comparing the performance characteristics of both methods, it was concluded that the HPLC-FLD method is more acceptable for the analysis of hydroxychloroquine because it allows the determination of lower concentrations of the investigated drug. Both methods were used to monitor photolytic and photocatalytic degradation of hydroxychloroquines. In the second part, photolytic and photocatalytic degradation of hydroxychloroquine was investigated using TiO2 as photocatalysts in the form of thin film and suspensions and various sources of radiation: LED lamps at wavelengths of 365 and 405 nm, solar - like lamp and halogen lamp. The results of photolytic and photocatalytic degradation of hydroxychloroquines have shown that they are not subject to photolytic degradation, and photocatalytic degradation is faster with the photocatalyst present in the form of suspension. Photocatalytic degradation kinetics follows the kinetics of the first order. Using the validated HPLC-FLD method, four degradation products were detected during photocatalytic degradation by a 365 nm LED lamp, whilst during photocatalytic degradation with 405 nm LED lamp, there were three degradation products. Using the validated HPLC-DAD method, two degradation products were detected during photocatalytic degradation by a 405 nm LED lamp, whilst during photocatalytic degradation with 365 nm LED lamp did not detect any degradant products

Chromatographic methods for the monitoring of photocatalytic degradation of hydroxychloroquine

U ovom radu razvijene su metode HPLC-DAD i HPLC-FLD za praćenje farmaceutika hidroksiklorokina u uzorcima vode. U okviru validacije razvijenih metoda ispitana je linearnost, osjetljivost i točnost, te su određene granice detekcije i kvantifikacije i radno područje metoda. Usporedbom izvedbenih značajki obje metode zaključeno je da je metoda HPLC-FLD prihvatljivija za analizu hidroksiklorokina jer omogućava određivanje nižih koncentracija ispitivanog farmaceutika. Obje razvijene metode primijenjene su za praćenje fotolitičke i fotokatalitičke razgradnje hidroksiklorokina. U drugom dijelu rada ispitana je fotolitička i fotokatalitička razgradnja hidroksiklorokina uz primjenu TiO2 kao fotokatalizatora u obliku tankog filma i suspenzije te različitih izvora zračenja: LED svjetiljka 365 nm i 405 nm, svjetiljka sa zračenjem sličnim Sunčevom i halogena svjetiljka. Rezultati fotolitičke i fotokatalitičke razgradnje hidroksiklorokina pokazali su da nije podložan fotolitičkoj razgradnji, a fotokatalitička razgradnja brža je uz fotokatlizator prisutan u obliku suspenzije. Kinetika fotokatalitičke razgradnje slijedi kinetiku prvog reda. Validiranom metodom HPLC-FLD uočeno je nastajanje četiri razgradna produkta tijekom fotokatalitičke razgradnje LED svjetiljkom 365 nm, dok se tijekom fotoktalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm javljaju tri razgradna produkta. Validiranom metodom HPLC-DAD uočeno je nastajanje dva razgradna produkta tijekom fotokatalitičke razgradnje uz osvjetljavanje LED svjetiljkom 405 nm, dok validiranom metodom uz osvjetljavanje LED svjetiljkom 365 nm nisu detektirani razgradni produkti.In this paper, HPLC-DAD and HPLC-FLD methods have been developed to monitor the hydroxylchloroquine pharmaceuticals in water samples. Within the validation of the methods developed, linearity, sensitivity and accuracy were examined, and the limits of detection and quantification and the working range of the method were determined. By comparing the performance characteristics of both methods, it was concluded that the HPLC-FLD method is more acceptable for the analysis of hydroxychloroquine because it allows the determination of lower concentrations of the investigated drug. Both methods were used to monitor photolytic and photocatalytic degradation of hydroxychloroquines. In the second part, photolytic and photocatalytic degradation of hydroxychloroquine was investigated using TiO2 as photocatalysts in the form of thin film and suspensions and various sources of radiation: LED lamps at wavelengths of 365 and 405 nm, solar - like lamp and halogen lamp. The results of photolytic and photocatalytic degradation of hydroxychloroquines have shown that they are not subject to photolytic degradation, and photocatalytic degradation is faster with the photocatalyst present in the form of suspension. Photocatalytic degradation kinetics follows the kinetics of the first order. Using the validated HPLC-FLD method, four degradation products were detected during photocatalytic degradation by a 365 nm LED lamp, whilst during photocatalytic degradation with 405 nm LED lamp, there were three degradation products. Using the validated HPLC-DAD method, two degradation products were detected during photocatalytic degradation by a 405 nm LED lamp, whilst during photocatalytic degradation with 365 nm LED lamp did not detect any degradant products

Development of photocatalytic nanocomposite based on titanium dioxide and reduced graphene oxide

U ovom radu pripravljen je grafenov oksid (GO) oksidacijom prirodnog grafita (≤50 μm) koristeći Hummersovu metodu. Hidrotermalnom/solvotermalnom metodom te naknadnom toplinskom obradom pri 300 °C pripravljene su nanočestice nanokompozita na bazi titanijeva dioksida i reduciranoga grafenova oksida (TiO2@rGO) s masenim udjelom rGO od 4, 8 i 16 mas.%. Sintetizirani fotokatalizatori karakterizirani su različitim strukturnim, morfološkim i optičkim metodama karakterizacije nanomaterijala. Adsorpcija i fotokatalitička aktivnost pripremljenih nanočestica TiO2 i TiO2@rGO nanokompozita ispitana je na procesu djelotvornosti razgradnje vodene otopine bojila metilenskog modrila. Praćen je utjecaj početne koncentracije i pH vrijednosti otopine bojila, koncentracije katalizatora, vodene matrice i izvora zračenja. Ispitana je mogućnosti ponovne upotrebe TiO2@rGO fotokatalizatora u tri ciklusa. Dobiveni rezultati karakterizacije pripravljenih materijala ukazuju na postojanje interakcija između TiO2 i rGO odnosno Ti–O–C veze što potvrđuje uspješnu pripravu TiO2@rGO nanokompozita. Nadalje, dodatkom rGO povećana je specifična površina, smanjen je energetski procjep i povećana je djelotvornost fotokatalitičke razgradnje metilenskog modrila u odnosu na nanočestice TiO2. Određena je optimalna količina (8 mas.%) reduciranoga grafenova oksida u nanokompozitu na bazi titanijeva dioksida i reduciranoga grafenova oksida za učinkovitu fotokatalitičku razgradnju metilenskog modrila. Utvrđeno je da je optimalna fotokatalitička djelotvornost razgradnje metilenskog bojila postignuta 99,20 % za početnu koncentraciju bojila od 10 mg·L–1 i početnu koncentraciju katalizatora od 0,5 g·L–1 pri 22 ± 0.5 °C. Ustanovljeno je da je model pseudo prvog reda prihvatljiv za opis kinetike fotokatalitičke razgradnje metilenskog modrila primjenom pripravljenih fotokatalizatora. Rezultati su pokazali da se pripravljeni TiO2@rGO_8 mas.% nanokompozit može koristiti u tri uzastopna ciklusa uz zadržavanje fotokatalitičke aktivnost preko 90 %.In this study, graphene oxide was prepared by the oxidation of natural graphite flakes (≤50 μm) using Hummer's method. Nanoparticles of nanocomposites based on titanium dioxide and reduced graphene oxide (TiO2@rGO) with percentage weights of rGO of 4, 8, and 16 wt.%, were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The synthesised photocatalysts were characterised by various structural, morphological, and optical characterisation methods for nanomaterials. The adsorption and photocatalytic activity of the prepared TiO2@rGO nanocomposite were tested on their efficacy in the removal of methylene blue dye from water. Furthermore, the photocatalytic efficiency of the prepared photocatalysts was tested by changing various parameters such as the irradiation source, the concentration of the catalyst, the initial concentration of the dye model solution, the pH of the dye solution and the water matrix. The possibility of reusing TiO2@rGO photocatalyst for three cycles was tested. The results obtained for the characterisation of the prepared materials indicate the existence of interactions between TiO2 and rGO, i.e., the Ti–O–C bond, which confirms the successful preparation of TiO2@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic efficiency of methylene blue removal from water compared to TiO2 nanoparticles. The results of photocatalytic activity indicate that the amount of rGO in the prepared TiO2@rGO nanocomposites plays a significant role in the application of different photocatalytic parameters. The optimal amount (8 wt.%) of reduced graphene oxide in the nanocomposite for the efficient photocatalytic decomposition of methylene blue was determined. It was determined that the optimal photocatalytic efficiency of methyl dye degradation was achieved 99.20 % for an initial dye concentration of 10 mg·L– 1 and an initial catalyst concentration of 0.5 g·L– 1 at 22 ± 0.5 °C. It was found that the pseudo first-order model is acceptable for describing the kinetics of the photocatalytic decomposition of methylene blue using the prepared photocatalysts. The results showed that the TiO2@rGO_8 wt.% nanocomposite can be used for three consecutive cycles while maintaining photocatalytic activity over 90 %

Development of photocatalytic nanocomposite based on titanium dioxide and reduced graphene oxide

U ovom radu pripravljen je grafenov oksid (GO) oksidacijom prirodnog grafita (≤50 μm) koristeći Hummersovu metodu. Hidrotermalnom/solvotermalnom metodom te naknadnom toplinskom obradom pri 300 °C pripravljene su nanočestice nanokompozita na bazi titanijeva dioksida i reduciranoga grafenova oksida (TiO2@rGO) s masenim udjelom rGO od 4, 8 i 16 mas.%. Sintetizirani fotokatalizatori karakterizirani su različitim strukturnim, morfološkim i optičkim metodama karakterizacije nanomaterijala. Adsorpcija i fotokatalitička aktivnost pripremljenih nanočestica TiO2 i TiO2@rGO nanokompozita ispitana je na procesu djelotvornosti razgradnje vodene otopine bojila metilenskog modrila. Praćen je utjecaj početne koncentracije i pH vrijednosti otopine bojila, koncentracije katalizatora, vodene matrice i izvora zračenja. Ispitana je mogućnosti ponovne upotrebe TiO2@rGO fotokatalizatora u tri ciklusa. Dobiveni rezultati karakterizacije pripravljenih materijala ukazuju na postojanje interakcija između TiO2 i rGO odnosno Ti–O–C veze što potvrđuje uspješnu pripravu TiO2@rGO nanokompozita. Nadalje, dodatkom rGO povećana je specifična površina, smanjen je energetski procjep i povećana je djelotvornost fotokatalitičke razgradnje metilenskog modrila u odnosu na nanočestice TiO2. Određena je optimalna količina (8 mas.%) reduciranoga grafenova oksida u nanokompozitu na bazi titanijeva dioksida i reduciranoga grafenova oksida za učinkovitu fotokatalitičku razgradnju metilenskog modrila. Utvrđeno je da je optimalna fotokatalitička djelotvornost razgradnje metilenskog bojila postignuta 99,20 % za početnu koncentraciju bojila od 10 mg·L–1 i početnu koncentraciju katalizatora od 0,5 g·L–1 pri 22 ± 0.5 °C. Ustanovljeno je da je model pseudo prvog reda prihvatljiv za opis kinetike fotokatalitičke razgradnje metilenskog modrila primjenom pripravljenih fotokatalizatora. Rezultati su pokazali da se pripravljeni TiO2@rGO_8 mas.% nanokompozit može koristiti u tri uzastopna ciklusa uz zadržavanje fotokatalitičke aktivnost preko 90 %.In this study, graphene oxide was prepared by the oxidation of natural graphite flakes (≤50 μm) using Hummer's method. Nanoparticles of nanocomposites based on titanium dioxide and reduced graphene oxide (TiO2@rGO) with percentage weights of rGO of 4, 8, and 16 wt.%, were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The synthesised photocatalysts were characterised by various structural, morphological, and optical characterisation methods for nanomaterials. The adsorption and photocatalytic activity of the prepared TiO2@rGO nanocomposite were tested on their efficacy in the removal of methylene blue dye from water. Furthermore, the photocatalytic efficiency of the prepared photocatalysts was tested by changing various parameters such as the irradiation source, the concentration of the catalyst, the initial concentration of the dye model solution, the pH of the dye solution and the water matrix. The possibility of reusing TiO2@rGO photocatalyst for three cycles was tested. The results obtained for the characterisation of the prepared materials indicate the existence of interactions between TiO2 and rGO, i.e., the Ti–O–C bond, which confirms the successful preparation of TiO2@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic efficiency of methylene blue removal from water compared to TiO2 nanoparticles. The results of photocatalytic activity indicate that the amount of rGO in the prepared TiO2@rGO nanocomposites plays a significant role in the application of different photocatalytic parameters. The optimal amount (8 wt.%) of reduced graphene oxide in the nanocomposite for the efficient photocatalytic decomposition of methylene blue was determined. It was determined that the optimal photocatalytic efficiency of methyl dye degradation was achieved 99.20 % for an initial dye concentration of 10 mg·L– 1 and an initial catalyst concentration of 0.5 g·L– 1 at 22 ± 0.5 °C. It was found that the pseudo first-order model is acceptable for describing the kinetics of the photocatalytic decomposition of methylene blue using the prepared photocatalysts. The results showed that the TiO2@rGO_8 wt.% nanocomposite can be used for three consecutive cycles while maintaining photocatalytic activity over 90 %

Development of photocatalytic nanocomposite based on titanium dioxide and reduced graphene oxide

U ovom radu pripravljen je grafenov oksid (GO) oksidacijom prirodnog grafita (≤50 μm) koristeći Hummersovu metodu. Hidrotermalnom/solvotermalnom metodom te naknadnom toplinskom obradom pri 300 °C pripravljene su nanočestice nanokompozita na bazi titanijeva dioksida i reduciranoga grafenova oksida (TiO2@rGO) s masenim udjelom rGO od 4, 8 i 16 mas.%. Sintetizirani fotokatalizatori karakterizirani su različitim strukturnim, morfološkim i optičkim metodama karakterizacije nanomaterijala. Adsorpcija i fotokatalitička aktivnost pripremljenih nanočestica TiO2 i TiO2@rGO nanokompozita ispitana je na procesu djelotvornosti razgradnje vodene otopine bojila metilenskog modrila. Praćen je utjecaj početne koncentracije i pH vrijednosti otopine bojila, koncentracije katalizatora, vodene matrice i izvora zračenja. Ispitana je mogućnosti ponovne upotrebe TiO2@rGO fotokatalizatora u tri ciklusa. Dobiveni rezultati karakterizacije pripravljenih materijala ukazuju na postojanje interakcija između TiO2 i rGO odnosno Ti–O–C veze što potvrđuje uspješnu pripravu TiO2@rGO nanokompozita. Nadalje, dodatkom rGO povećana je specifična površina, smanjen je energetski procjep i povećana je djelotvornost fotokatalitičke razgradnje metilenskog modrila u odnosu na nanočestice TiO2. Određena je optimalna količina (8 mas.%) reduciranoga grafenova oksida u nanokompozitu na bazi titanijeva dioksida i reduciranoga grafenova oksida za učinkovitu fotokatalitičku razgradnju metilenskog modrila. Utvrđeno je da je optimalna fotokatalitička djelotvornost razgradnje metilenskog bojila postignuta 99,20 % za početnu koncentraciju bojila od 10 mg·L–1 i početnu koncentraciju katalizatora od 0,5 g·L–1 pri 22 ± 0.5 °C. Ustanovljeno je da je model pseudo prvog reda prihvatljiv za opis kinetike fotokatalitičke razgradnje metilenskog modrila primjenom pripravljenih fotokatalizatora. Rezultati su pokazali da se pripravljeni TiO2@rGO_8 mas.% nanokompozit može koristiti u tri uzastopna ciklusa uz zadržavanje fotokatalitičke aktivnost preko 90 %.In this study, graphene oxide was prepared by the oxidation of natural graphite flakes (≤50 μm) using Hummer's method. Nanoparticles of nanocomposites based on titanium dioxide and reduced graphene oxide (TiO2@rGO) with percentage weights of rGO of 4, 8, and 16 wt.%, were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The synthesised photocatalysts were characterised by various structural, morphological, and optical characterisation methods for nanomaterials. The adsorption and photocatalytic activity of the prepared TiO2@rGO nanocomposite were tested on their efficacy in the removal of methylene blue dye from water. Furthermore, the photocatalytic efficiency of the prepared photocatalysts was tested by changing various parameters such as the irradiation source, the concentration of the catalyst, the initial concentration of the dye model solution, the pH of the dye solution and the water matrix. The possibility of reusing TiO2@rGO photocatalyst for three cycles was tested. The results obtained for the characterisation of the prepared materials indicate the existence of interactions between TiO2 and rGO, i.e., the Ti–O–C bond, which confirms the successful preparation of TiO2@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic efficiency of methylene blue removal from water compared to TiO2 nanoparticles. The results of photocatalytic activity indicate that the amount of rGO in the prepared TiO2@rGO nanocomposites plays a significant role in the application of different photocatalytic parameters. The optimal amount (8 wt.%) of reduced graphene oxide in the nanocomposite for the efficient photocatalytic decomposition of methylene blue was determined. It was determined that the optimal photocatalytic efficiency of methyl dye degradation was achieved 99.20 % for an initial dye concentration of 10 mg·L– 1 and an initial catalyst concentration of 0.5 g·L– 1 at 22 ± 0.5 °C. It was found that the pseudo first-order model is acceptable for describing the kinetics of the photocatalytic decomposition of methylene blue using the prepared photocatalysts. The results showed that the TiO2@rGO_8 wt.% nanocomposite can be used for three consecutive cycles while maintaining photocatalytic activity over 90 %

Influence of Ageing on Abrasion Volume Loss, Density, and Structural Components of Subfossil Oak

Subfossil oak wood has spent centuries or millennia in the aquatic medium (rivers, lakes, bogs, etc.) and, due to water anoxic conditions, its decomposition is very slow. As a result of its long residing in specific conditions, its chemical composition, appearance, as well as mechanical and tribological properties have changed. Because of its aesthetic and mechanical properties, subfossil wood is very attractive and often used to produce valuable objects. The main objective of this study was to test how abrasion wear resistance of subfossil oak is affected by ageing. The effects of ageing on wood density and on the structure of lignin and cellulose were tested, as well as the loss of volume during abrasion in correlation with these changes. A study was conducted on samples of recent (regular) pedunculate oak wood and on six subfossil pedunculate oak samples in the age range of 890 and nearly 6000 years. Abrasion wear resistance was expressed through the loss of volume recorded using the Taber abraser. The smallest abrasion volume loss was measured for the recent oak specimens. Linear regression analyses showed that there was a very strong negative linear relationship between the age of subfossil oak and its abrasion volume loss. There was also a strong, but positive and significant linear correlation between subfossil oak age and density. Ageing also affected the structural composition of wood. Results obtained by Fourier Transform Infrared spectroscopy indicated a reduction of the relative crystalline fraction of subfossil wood in recent oak. The degradation of lignin in subfossil oak samples progressed more slowly over time than cellulose degradation. There was a negative correlation between age and the ratio of cellulose and lignin degradation; however, that relationship was found statistically insignificant. Similar results were obtained for the relationship between abrasion wear resistance and changes in the structural composition of the studied samples of subfossil oak wood