Absence Of Photocatalyst Research Articles

Gold-decorated Fe3O4 nanoparticles for efficient photocatalytic degradation of ampicillin: a chemometrics investigation

Wastewater treatment for lowering down the amount of antibiotic drugs in environment is essential for preventing their harmful effects in the ecosystem and for diminishing the growing bacterial resistance. Here, gold-decorated Fe3O4 nanoparticles (NPs) were used for efficient photocatalytic degradation of ampicillin, investigated by UV/Vis absorbance spectrometry. The absorbance data matrices recorded in the course of reactions were analyzed using multivariate curve resolution-alternative least squares as a power chemometrics method. The resolved concentration profiles were composed of three intermediate species and one final product. The concentration profiles were fitted to a first-order kinetics and for the photodegradation experiments run (1) in the absence of photocatalyst, (2) in the presence of Fe3O4 NPs and (3) in the presence of Au-decorated Fe3O4 NPs, the rate constants of 0.023, 0.041 and 0.055 min−1 were obtained, respectively. We found that ampicillin undergoes fast photocatalytic degradation reaction, so that, in the presence of Fe3O4 NPs and Au-decorated magnetic NPs, it was completely converted to its photodegradation product in a few min (35 and 25 min, respectively). The results obtained by chemometrics analysis of the absorbance data agreed with those obtained by capillary electrophoresis.

Intrinsic and Catalyzed Photochemistry of Phenylvinylketone for Wavelength‐Sensitive Controlled Polymerization

AbstractReversible addition‐fragmentation chain transfer (RAFT) photopolymerization of phenylvinylketone (PVK) is investigated. The polymerization is investigated both in the presence of two photocatalysts (iridium tris(phenylpyridine (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP)). The polymerization was efficient in the absence of photocatalyst, and accelerated by Ir(ppy)3, whereas ZnTPP was found to lead to retardation of polymerization. In all cases, well‐controlled polymers were synthesized with linear growth in Mn with conversion and narrow molecular weight distributions. The observed photopolymerization kinetics were consistent with a Norrish Type 1 reaction of PVK to give two radicals. The polymerization kinetics were investigated as a function of wavelength, with the reaction rate being fastest with blue irradiation (440 nm), which is surprisingly far from the absorption maximum of PVK and Ir(ppy)3. Photodegradation of PVK was observed under UV irradiation, but the polymers were stable against visible light.

Visible‐Light‐Induced Hydroxysulfurization and Alkoxysulfurization of Styrenes in the Absence of Photocatalyst: Synthesis of β‐Hydroxysulfides and β‐Alkoxysulfides

AbstractWe developed hydroxysulfurization and alkoxysulfurization of styrenes using a visible‐light synthetic strategy in the absence of photocatalyst and oxidant. This strategy provided the corresponding β‐hydroxysulfides and β‐alkoxysulfides in moderate to good yields with high regioselectivity. The reaction was tolerated by a wide range of functional groups. This is the first example of ArSSAr/CBr4 system has been introduced into organic transformation.magnified image

Visible‐Light‐Promoted Dearomative Fluoroalkylation of β‐Naphthols through Intermolecular Charge Transfer

AbstractThe first visible‐light‐promoted dearomative fluoroalkylation of β‐naphthols was realized without the assistance of any transition‐metal catalysts or external photosensitizers. Inexpensive fluoroalkyl iodides were directly used as efficient fluoroalkylation reagents under very mild reaction conditions. The scope of this process was found to be general and broad, and both trifluoromethyl and perfluoroalkyl groups (‐C4F9, ‐C6F13, and ‐C8F17) were installed in excellent yields. Preliminary mechanistic studies suggest that visible‐light‐promoted intermolecular charge transfer within the naphtholate–fluoroalkyl iodide electron donor–acceptor (EDA) complex induces a single electron transfer in the absence of photocatalysts.

Visible-Light-Promoted Dearomative Fluoroalkylation of β-Naphthols through Intermolecular Charge Transfer.

The first visible-light-promoted dearomative fluoroalkylation of β-naphthols was realized without the assistance of any transition-metal catalysts or external photosensitizers. Inexpensive fluoroalkyl iodides were directly used as efficient fluoroalkylation reagents under very mild reaction conditions. The scope of this process was found to be general and broad, and both trifluoromethyl and perfluoroalkyl groups (-C4 F9 , -C6 F13 , and -C8 F17 ) were installed in excellent yields. Preliminary mechanistic studies suggest that visible-light-promoted intermolecular charge transfer within the naphtholate-fluoroalkyl iodide electron donor-acceptor (EDA) complex induces a single electron transfer in the absence of photocatalysts.

Photocatalytic degradation of Orange G using sepiolite-TiO2 nanocomposites: Optimization of physicochemical parameters and kinetics studies

Highly photoactive nanocomposites Sep-TiO2 with various ratios of Ti/Sep were prepared by a novel microwave-hydrothermal method and were compared for their photocatalytic activity. The catalyst with the Ti/Sep ratio of 40 mmol/g showed the highest photodegradation activity on account of its relatively intact sepiolite structure and more anatase active sites. The effects of operational conditions, including photocatalyst amount, initial dye concentration and pH on photocatalytic degradation performance were analyzed and optimized, which demonstrated low and negligible photodegradation efficiency in the presence of sepiolite only and in the absence of photocatalyst, respectively. The photocatalytic degradation kinetics under different reaction conditions was elucidated by modeling. The results showed that the photocatalytic degradation of Orange G could be described by the modified Langmuir-Hinshelwood model. The photocatalytic degradation process fits into first-order kinetics for most of the operational parameters, while follows zero-order kinetics for the condition of high dye concentration. The apparent rate constants kapp for each degradation reaction were calculated by fitting the model to experimental data and the highest value was obtained at catalyst dosage 0.8 g/L, initial dye concentration 10 mg/L and pH = 3. Moreover, the recycling experiments confirmed the stability of the catalyst.

Natural RAFT Polymerization: Recyclable-Catalyst-Aided, Opened-to-Air, and Sunlight-Photolyzed RAFT Polymerizations.

The successful sunlight-photolyzed reversible addition-fragmentation chain transfer (RAFT) photopolymerization can be reversibly activated and deactivated by irradiation with sunlight in the absence of photocatalyst and photoinitiator. In the present work, the thiocarbonylthio compounds (dithiobenzoate, trithiocarbonate, and xanthate) can all be employed to carry out the polymerization under sunlight irradiation acting as an initiator, chain transfer agent, and termination agent. Moreover, it was demonstrated that the recyclable-catalyst-aided, opened-to-air, and sunlight-photolyzed RAFT (ROS-RAFT) polymerizations can be successfully carried out to fabricate precise and predictable polymers in the presence of the recyclable magnetic semiconductor nanoparticles (NPs). The oxygen tolerance is likely attributed to a specific interaction between NPs and oxygen.

Combined biological and photocatalytic treatment of real coke oven wastewater

Wastewater generated from coke oven industries contains highly toxic organic and inorganic compounds. In the present study, biological reactors were integrated in sequence of anaerobic–aerobic–anoxic and tested with real coke oven wastewater obtained from a Steel Plant located in India. Among several pretreatment methods, coagulation of raw CWW was found to be effective. COD removal efficiency of 78.5% was achieved by the integrated bioreactor system after coagulation of CWW with 1000mg/L of alum. The effluent COD, NH4-N and TCN concentration from the integrated bioreactors was 420, 152 and 20mg/L, respectively. It was observed that 420mg/L of COD present in the effluent after integrated bio treatment was degraded in less than 4h to minimum COD concentration of 94mg/L using UV–TiO2 photocatalysis. In absence of photocatalyst (TiO2), there was no COD reduction from the bio treated effluent. Similarly, there was insignificant reduction in COD from the raw CWW using photocatalysis without biological treatment. Considerable COD reduction (78.5%) was observed only in the wastewater subjected to integrated biological system. The overall COD removal efficiency of the combined treatment system was found to be 96.2%, which resulted in an effluent COD concentration less than 94mg/L.

HsDNA groove binding, photocatalytic activity, and in vitro breast and colon cancer cell reducing function of greener SeNPs.

Selenium nanoparticles (SeNPs) have attracted great attention because of their superior optical properties and wide utilization in biological and biomedical studies. This paper reports an environmentally benign procedure of greener monodispersible SeNP synthesis using the reducing power of Trigonella foenum-graecum extract, characterization and their protective effect against unfolded (Herring sperm DNA) hsDNA. We investigated the anti-cancer activity of SeNPs against MCF-7, MDA MB 435 and COLO-205 cells. The photocatalytic activity of SeNPs was investigated for the degradation of a Sunset Yellow FCF (SYFCF) dye using ultraviolet-B light. The reduction of the Se ion to SeNPs was monitored by ultraviolet-visible spectroscopy (UV-vis). The size and morphology of the SeNPs were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and Dynamic Light Scattering (DLS). The SeNPs were stable, and the diameter was homogeneous at around 5-12 nm. Interactions of various concentrations of SeNPs with hsDNA were systematically investigated by UV-vis, fluorescence, circular dichroism (CD), polarimetry and FTIR spectroscopy under physiological conditions. The results from fluorescence spectroscopy indicated that SeNPs quenched the fluorescence intensity of hsDNA with increasing concentrations. The modified Stern-Volmer quenching rate constant Ksv, binding constant K and binding sites n at different temperatures and the corresponding thermodynamic parameters ΔH°, ΔG° and ΔS° were calculated. Hoechst 33258 and methyl green (MG) site markers, melting experiment (Tm), viscosity measurements and sequence specificity verification by DNA bases clarified that SeNPs bind to hsDNA via a groove site. The rate of photocatalytic degradation of the SYFCF dye in the presence and absence of photocatalysts (SeNPs) was studied using UV-vis, the results showed appreciable degradation of the SYFCF dye. Our results suggested that nano Se can be used as a promising selenium species with potential application in cancer treatment. These nanoparticles were found to be the most active cytotoxic agent prepared in a new green synthesis manner, causing >50% inhibition of MCF-7, MDA MB-435 and COLO-205 cell proliferation at concentrations <10(-7) M. Hence these SeNPs could be recognized as promising materials for biomedical applications.

NOx de-pollution by hardened concrete and the influence of activated charcoal additions

The atmospheric pollution by nitrogen oxides affects the health of millions of people located in urban areas. Our work demonstrates that, even in the absence of photocatalysts, concrete walls can strongly absorb NO2 and limit the intensity of pollution peaks. Our results show that concretes can continuously absorb a significant fraction of NO2 from the surrounding atmosphere over long periods, probably due to a reaction with strongly alkaline cement hydrates. Moreover, the introduction of a small amount of activated charcoal into the concrete mix can significantly enhance and prolong this NO2 absorption without greatly increasing total porosity or decreasing strength. We hypothesize that the NO2 is adsorbed irreversibly by a neutralization reaction with the alkaline aqueous solution covering the surfaces of the hydrates and the activated charcoal. Simple calculations suggest that walls made of activated charcoal concrete could ameliorate the problem of NO2 pollution peaks in road tunnels and parking garages.

Photo-degradation of malachite green in mudfish tissues — investigation of UV-induced photo-degradation

Ultraviolet (UV) light induced photo-degradation of malachite green (MG) was investigated in the absence of photocatalysts. Photo-degraded intermediates were identified using LC with visible detection and LCelectrospray ionization-MS. Using this analysis, mechanisms for the MG decomposition in aqueous solution and in mudfish tissue were suggested. In aqueous condition, N-de-methylation and the decomposition of the conjugated structures were mainly observed. On the other hand, MG levels in mudfish continuously decreased until they reached a plateau owing to the decomposition of the conjugated structures. These results show that some chemicals in fish tissues could be photo-degraded by UV light without photocatalysts.

UV light exposure of aqueous graphene oxide suspensions to promote their direct reduction, formation of graphene–metal nanoparticle hybrids and dye degradation

The use of UV light to trigger different processes involving graphene oxide sheets suspended in aqueous medium at room temperature has been investigated. These processes include (1) deoxygenation of the sheets in the absence of photocatalysts, reducing agents and stabilizers, (2) selective nucleation and growth of metal nanoparticles on the sheets to yield graphene-based hybrids and (3) decomposition of the dye molecule rhodamine B in the presence of only graphene oxide. Photoinduced heating of the suspended graphene oxide sheets by intense UV irradiation (∼1 W cm −2 delivered at the surface of the dispersion) was interpreted to generate at high temperature and reactive environment strictly localized at the sheets and their immediate aqueous medium, which in turn brings about the mentioned processes. In addition to providing a simple route toward reduction of graphene oxide dispersions, the present results suggest that intense UV light can be used to promote reactions at ambient conditions with this material that would otherwise require high temperatures, chemical reactants and/or catalysts.

Photodegradation of aromatic amines by Ag-TiO2 photocatalyst

The photocatalytic degradation of ortho, para and meta-nitroanilines (ONA, PNA and MNA) was investigated by Ag-TiO2 suspension. The effect of some parameters such as the amount of photocatalyst, irradiation time of UV light, flow rate of O2, pH, and temperature for the Ag-TiO2 photocatalyst was also examined. Degradation of amines was small when the reaction was carried out in the absence of photocatalyst, and negligible in the absence of the UV light. Degradation rate of aniline derivatives decreases with increasing O2 in the system. The effect of pH indicated that effective degradation occurred in alkaline conditions. Degradation kinetics of these aromatic amines can be described by Langmuir-Hinshelwood equation and shows pseudo-first order law.

Efficiency of Clay−TiO2 Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Clay-supported TiO2 photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a benchtop photocatalytic flow reactor was used to evaluate the efficiency of hectorite-TiO2 and kaolinite-TiO2, two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (lamda(max) = 365 nm) or UVC (lamda(max) = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay-Ti02 composites was compared with that of pure TiO2 (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO2 composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of approximately 170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33, and 66% relative humidity (RH). Toluene concentrations were determined by collecting Tenax-TA sorbent tubes downstream of the reactor, with subsequent thermal desorption--GC/MS analysis. The fraction of toluene removed, %R, and the reaction rate, Tr, were calculated for each experimental condition from the concentrations measured with and without UV irradiation. Use of UVC light (UV/TiO2/O3) led to overall higher reactivity, which can be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, Tr/Ilamda,the UV/TiO2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO2 (P25 and Hecto-TiO2), but notfor Kao-TiO2. In all cases, reaction rates peaked at 10% RH, with Tr values between 10 and 50% higherthan those measured under dry air. However, a net inhibition was observed as RH increased to 33% and 66%, indicating that water molecules competed effectively with toluene for reactive surface sites and limited the overall photocatalytic conversion. Compared to P25, inhibition by coadsorbed water was less significant for Kao-TiO2 samples, but was more dramatic for Hecto-TiO2 due to the high water uptake capacity of hectorite.

Effect of UVA irradiance on photocatalytic and UVA inactivation of Bacillus cereus spores

The current study is the first to delineate the contribution of photocatalysis to inactivation of Bacillus cereus endospores on dry surfaces over a broad range (0–153 W/m 2) of UVA irradiance. Inactivation of spores at low UVA irradiance (30 W/m 2) was primarily due to photocatalysis, whereas at higher UVA irradiance inactivation was primarily due to UV alone. A linear relationship between UVA irradiance and the rate of spore inactivation was observed in the absence of photocatalyst. The rate of photocatalytic inactivation was non-linear with respect to UVA irradiance, exhibiting a maximum at 30 W/m 2.

Photochemical and photocatalytic degradation of salicylic acid with hydrogen peroxide over TiO 2/SiO 2 fibres

The effect of hydrogen peroxide on the photo-oxidation of salicylic acid (SA) in aqueous solutions under UV-irradiation was investigated in both purely homogeneous and photocatalytic conditions. Results obtained show that in absence of photocatalyst and under UV-irradiation, the SA degradation rate increases with increasing the amount of hydrogen peroxide added, although for high concentrations of H 2O 2 the enhancement of the activity is progressively attenuated. In the case of the photocatalytic degradation, nanocrystallites of anatase immobilised over SiO 2 fibres were used as catalyst. In the present of TiO 2/SiO 2, the addition of hydrogen peroxide results in almost a three-fold increment of the photoactivity at low concentration (29.1 mM). In contrast, when the amount of H 2O 2 added exceeds certain limit, the rate of SA removal becomes slightly lower than those measured in absence of photocatalyst. A simple kinetic model which considers the summation of both photochemical and photocatalytic contributions is used to account for the dependence of the rate on the H 2O 2 concentration. The efficiency of the SA mineralization was also evaluated by monitoring the evolution of total organic carbon (TOC) with irradiation time. In this respect, remarkable differences are found when comparing pure photochemical degradation, which only reduce the TOC concentration in about a 3% after 300 min of irradiation, with the photocatalytic treatment, which achieve a 38% of SA mineralization in the same period.

Photolytic dechlorination of 4-chlorophenol in O 2-saturated aqueous solutions in the absence of photocatalysts or additives using ArF ∗ (193 nm) and KrF ∗ (248 nm) excimer lasers

One of the toxic products from chlorine bleaching of wood pulp is 4-chlorophenol (4-CP). Detoxification of such compounds usually requires their dechlorination. The present study involves a fairly detailed comparison of the attempt and success of the photolytic dechlorination of 4-CP in O 2-saturated aqueous solutions using ArF ∗ (193 nm) and KrF ∗ (248 nm) excimer laser radiation at higher (1.1 × 10 −2 M) and lower (4.5 × 10 −4 M) starting substrate concentrations and comparisons of quantum yield (φ), product distributions, etc. At the higher starting substrate concentration (1.1 × 10 −2 M) the average initial quantum yields, i.e. early in the reaction process, for the disappearance of 4-CP (φ ≈2 0.30) and for the generation of chloride ions (φ ≈2 0.25) were about the same for both 193 and 248 nm radiation. However, when the number of photons absorbed ( n) became greater than about 3 × 10 20, more chloride ions (higher φ) were generated with the 193 nm radiation than with the 248 nm radiation. Oligomers were the major products for both wavelengths of radiation, but the quantity of oligomers generated was greater using the 193 nm radiation. At 248 nm a significant amount of hydroquinone was generated, whereas hydroquinone was not detected with the 193 nm radiation. In addition, a significant amount of 4-chlorocatechol was generated during the direct photolysis of 4-CP using either wavelength of radiation. This is a new result for the photolysis of 4-CP at a wavelength longer than 193 nm in the absence of added H 2O 2. At the lower starting substrate concentration (4.5 × 10 −4 M) the average initial quantum yields for the disappearance of 4-CP (φ ≈2 0.55) and for the generation of chloride ions (φ ≈2 0.45) were both much greater using the 193 nm radiation than with the 248 nm radiation and 0.10 respectively). At 193 nm oligomers were still the major products generated, but the fraction of oligomeric products generated was less than the fraction at the higher substrate concentration. This is consistent with the fact that at the lower substrate concentration a significant amount of hydroquinone was generated at 193 nm, whereas it was not detected at this wavelength for the higher substrate concentration. During the 248 nm photolysis of 4-CP at this lower starting substrate concentration, hydroquinone was the only major product generated in these experiments. Oligomers were not observed at this lower substrate concentration using 248 nm radiation, whereas oligomers were generated at the higher substrate concentration. The results demonstrate the utility of using an excimer laser for the photolytic dechlorination of 4-CP without added photocatalysts or additives. It is also possible to suggest a number of explanations, given in the text, which are consistent with our findings.

Photodecomposition of isoproturon in the presence and absence of photocatalysts like H2O2and TiO2

Isoproturon was photolysed in presence and absence of H2O2 and TiO2 at different wave lengths (254 nm, 290 nm and 300–800 nm). The impact of H2O2 and TiO2 to enhance the photodegradation of isoproturon was established. Eight photoproducts were identified by GC‐MS. N‐demethylation, hydroxylation, dimerisation, deisopropylation, methylation of aryl amine, removal of dimethylamine followed by methoxylation were found to be the main processes during photoreaction.