Three-dimensional observations of the electric field distribution of variable frequency microwaves, and scaling-up organic syntheses.

Variable Frequency Microwave (VFM) radiation provides a solution to the inhomogeneity of the electric field in the cavity, which has long led to a decline in the reliability of microwave chemical data and its industrial utilization. Herein, we report in-situ three-dimensional experimental measurements of the electric field's uniform distribution of VFMs within a multimode cavity under high power conditions, and their subsequent comparison to Fixed Frequency Microwaves (FFM) that could only be assessed earlier through theoretical analysis. We also examine the consequences of changes in VFM irradiation conditions and elucidate the threshold at which VFM irradiation might prove beneficial in syntheses. With an ultimate focus on the use of VFM microwave radiation toward industrial applications, we carried out an effective synthesis of 4-methylbyphenyl (4-MBP) in the presence of palladium (the catalyst) supported on activated carbon particulates (Pd/AC), and revisited two principal objectives: (a) the effective suppression of discharge phenomena (formation of hot spots), and (b) synthesis scale-up using a 5-fold increase in sample quantity and a 7.5-fold larger reactor size (diameter) than otherwise used in earlier studies.

Uptake of nanoparticles from sunscreen physical filters into cells arising from increased environmental microwave radiation: increased potential risk of the use of sunscreens to human health.

This study examines the microwave chemical risks posed by photocatalysts present in sunscreens (physical filters) against the increasing use of microwaves (radio waves) in the environment, sometimes referred to as electronic smog. Specifically, the study assesses the damage caused by silica-coated physical filters (photocatalysts, TiO2⋅ and/or ZnO) contained in commercially available sunscreens and fresh silica-coated ZnO for sunscreens to mouse skin fibroblasts cells (NIH/3T3) evaluated in vitro by the life/death of cells using two types of electromagnetic waves: UV light and microwave radiation, and under simultaneous irradiation with both UV light and microwaves. Conditions of the electromagnetic waves were such as to be of lower light irradiance than that of UVA/UVB radiation from incident sunlight, and with microwaves near the threshold power levels that affect human health. The photocatalytic activity of the physical filters was investigated by examining the degradation of the rhodamine B (RhB) dye in aqueous media and by the damage caused to DNA plasmids from E. coli. Compared to the photocatalytic activity of ZnO and TiO2 when irradiated with UV light alone, a clear enhanced photocatalytic activity was confirmed upon irradiating these physical filters concurrently with UV and microwaves. Moreover, the uptake of these metal oxides into the NIH/3T3 cells led to the death of these cells as a result of the enhanced photocatalytic activity of the metal oxides on exposure to microwave radiation.

Development of a microwave-discharge light-emitting diode (MDLED): a novel UV source for the UV-driven microwave-assisted TiO2 photocatalytic treatment of contaminated wastewaters.

This brief article reports on the fabrication of a prototype novel semiconductor digital device, a microwave-discharge light-emitting diode (MDLED), consisting of an LED and a Schottky barrier diode encapsulated in a quartz ampoule. Coating the surface of this ampoule with TiO2 yielded a new photocatalytic TiO2 unit (MDLED-TiO2) for use in treating contaminated wastewaters. To the extent that this MDLED-TiO2 is driven only by microwave energy, there is no need for electric wires or electrical AC power. As much of the activity of TiO2 photocatalyst is enhanced and ultraviolet light emission is generated only by irradiating with microwaves, the MDLED-TiO2 affords a simple water treatment device as demonstrated in the present study. The digital device consisted of 14 pieces of MDLED-TiO2  units immersed into a model contaminated wastewater toward the decomposition of organic pollutants and sterilization of natural bacteria-contaminated wastewaters performed in an energy-saving manner simply by irradiating the wastewaters with microwaves.

Revisiting the BaBiO3 semiconductor photocatalyst: synthesis, characterization, electronic structure, and photocatalytic activity.

This article revisits the properties of BaBiO3 examined extensively in the last two decades because of its electronic properties as a superconductor and as a semiconductor photocatalyst. Solid-state syntheses of this bismuthate have often involved BaCO3 as the barium source, which may lead to the formation of BaBiO3/BaCO3 heterostructures that could have an impact on the electronic properties and, more importantly, on the photocatalytic activity of this bismuthate. Accordingly, we synthesized BaBiO3 by a solid-state route to avoid the use of a carbonate; it was characterized by XRD, SEM, and EDX, while elemental mapping characterized the composition and the morphology of the crystalline BaBiO3 and its thin films with respect to structure, optoelectronic, and photocatalytic properties. XPS, periodic DFT calculations, and electrochemical impedance spectroscopy ascertained the electronic and electrical properties, while Raman and DRS spectroscopies assessed the relevant optical properties. The photocatalytic activity was determined via the degradation of phenol in aqueous media. Although some results accorded with earlier studies, the newer electronic structural data on this bismuthate, together with the photocatalytic experiments carried out in the presence of selective radical trapping agents, led to elucidating some of the mechanistic details of the photocatalytic processes that previous views of the BaBiO3 band structure failed to address or clarify. Analytical refinement of the XRD data inferred the as-synthesized BaBiO3 adopted the C2/m symmetry rather than the I2/m structure reported earlier, while Tauc plots from DRS spectra yielded a bandgap of 2.05 eV versus the range of 1.1-2.25 eV reported by others; the corresponding flatband potentials were 1.61 eV (EVB) and - 0.44 eV (ECB). The photocatalytic activity of BaBiO3 was somewhat greater than that of the well-known Evonik P25 TiO2 photocatalyst under comparable experimental conditions.

Synthesis of Recyclable Magnetic Cellulose Nanofibers from Ionic Liquids for Practical Applications in Separation Science.

The present study focused on coupling cellulose nanofibers (alternative materials for plastics and metals) with a magnetic ionic liquid (synthesized by a microwave-assisted method) through mixing to yield magnetic cellulose nanofibers (MCNFs) that can be recycled by attracting them to a magnet. Accordingly, two types of ionic liquids were synthesized: (a) 1-butyl-3-methylimidazolium tetrachloroferrate(III) {[bmim] FeCl4} and (b) 1-glycidyl-3-methylimidazolium tetrachloroferrate {[glmi]FeCl4}, which were characterized by the fast atom bombardment mass spectrometry (FAB-MS) technique. Impregnation of the cellulose nanofibers with the {[bmim]FeCl4} ionic liquid caused the latter to be physically adsorbed onto the nanofibers to produce {MCNF@{[bmim]FeCl4}, whereas the corresponding {[glmi]FeCl4} ionic liquid was chemically bonded to the cellulose nanofibers to yield magnetic {MCNF@[glmi]FeCl4} nanofibers. Under the experimental conditions used, the corresponding magnetic moments were 0.222 A m2 kg-1 for {MCNF@ {[bmim]FeCl4} and 0.095 A m2 kg-1 for {MCNF@[glmi]FeCl4}.

Separation and Recombination of Photocarriers from Color Centers and Optically Silent Trap States from 100 to 450 K: The Halide Double Photochromic Perovskite Cs2AgBiBr6.

Compared to lead-based solar cells whose power conversion efficiency is 25.2%, the highest power conversion efficiency of a halide double Cs2AgBiBr6-based perovskite solar cell is less than 3%. It was therefore relevant to unravel the inherent reason(s) for such a low efficiency in the latter that may be related to trapping/detrapping of photocarriers. Accordingly, photocoloration and photobleaching phenomena occurring in the Cs2AgBiBr6 photochromic perovskite were examined from 100 to 450 K by diffuse reflectance spectroscopy (DRS). The separation and recombination of photogenerated charge carriers implicated both color centers and optically silent trap states within the bandgap. The processes were reversible subsequent to heating after illumination at 100 K but were mostly irreversible at 290 K. DRS spectral and kinetic measurements at T = 100-450 K were carried out after visible light illumination that further revealed the nature of the various charge carrier traps in Cs2AgBiBr6. Results confirmed the separation of photogenerated electrons and holes, with formation of the color centers identified as deep electron traps. Three different photoinduced color centers were responsible for the absorption bands observed at 1.78 (ab1), 1.39 (ab2), and 1.10 eV (ab3) at 100 K. Annealing of these electron-type color centers occurred in the temperature range of 100-450 K via recombination with holes in the valence band following their thermal release from the several hole traps. Application of a first-order kinetic model to the thermoprogrammed annealing (TPA) of the color centers' spectra yielded estimates of the activation energies of hole detrapping and lifetimes of trapped holes at room temperature. The irreversibility of photocoloration at 290 K was caused by the formation of new deep hole trap states.

In Search of the Driving Factor for the Microwave Curing of Epoxy Adhesives and for the Protection of the Base Substrate against Thermal Damage.

This study used controlled microwaves to elucidate the response of adhesive components to microwaves and examined the advantages of microwave radiation in curing epoxy adhesives. Curing of adhesives with microwaves proceeded very rapidly, even though each component of the adhesive was not efficiently heated by the microwaves. The reason the adhesive cured rapidly is that microwave heating was enhanced by the electrically charged (ionic) intermediates produced by the curing reaction. In contrast, the cured adhesive displayed lower microwave absorption and lower heating efficiency, suggesting that the cured adhesive stopped heating even if it continued to be exposed to microwaves. This is a definite advantage in the curing of adhesives with microwaves, as, for example, adhesives dropped onto polystyrene could be cured using microwave heating without degrading the polystyrene base substrate.

Photoluminescent Carbon Quantum Dots: Synthetic Approaches and Photophysical Properties.

A number of synthetic methodologies and applications of carbon quantum dots (CQDs) have been reported since they were first discovered nearly two decades ago. Unlike metal-based or semiconductor-based (e. g., metal chalcogenides) quantum dots (MSQDs), CQDs have the unique feature of being prepared through a variety of synthetic protocols, which are typically understood from considerations of reaction models and photoluminescence mechanisms. Consequently, this brief review article describes quantum dots, in general, and CQDs, in particular, from various viewpoints: (i) their definition, (ii) their photophysical properties, and (iii) the superiority of CQDs over MSQDs. Where possible, comparisons are made between CQDs and MSQDs. First, however, the review begins with a general brief description of quantum dots (QDs) as nanomaterials (sizes≤10 nm), followed by a short description of MSQDs and CQDs. Described subsequently are the various top-down and bottom-up approaches to synthesize CQDs followed by their distinctive photophysical properties (emission spectra; quantum yields, Φs).

Development of a Hg-free UV light source incorporating a Kr/Br2 gas, and its application for wastewater treatments.

Mercury lamps are typically the major light sources in water treatments. However, the use of mercury has raised some concerns with regard to the Minamata Convention on Mercury. As such, Hg-free microwave discharged electrodeless lamps (MDELs) that incorporate a rare gas and a halogen gas (R/H-MDEL) have been investigated with such Hg-free mixture filler gases as Kr/Cl2, Xe/Cl2, and Kr/Br2 (R/H). Of these, only the Kr/Br2-MDEL lamp is self-ignited at an inner pressure of 15 Torr when irradiated with microwave radiation. Accordingly, a novel Kr/Br2 three-layer MDEL (Kr/Br2-MDEL) photoreactor was fabricated to assess the optimal gas composition and gas pressure toward its performance vis-à-vis the treatment of model wastewaters contaminated with the tartrazine dye in aqueous media and with Escherichia coli (E. coli) bacteria. The extent of degradation of the tartrazine dye and sterilization of E. coli increased with irradiation time, with microwave radiation power (100, 200, and 300 W), and with increased sample flow rate 0.4 L min‒1 to 0.8 L min‒1. The tartrazine-contaminated wastewater was treated at a flow rate of 0.4 L min‒1 for 60 min of microwave irradiation by three different protocols that resulted in UV (62%) >> UV/ROS (24%) > ROS (0%); ROS denotes reactive oxygen species. After 5 min irradiation of the E.coli wastewater, also at 0.4 L min‒1, the order was UV (99.5%) ≈ UV/ROS (99.3%) >> ROS (14.5%). For comparison, the photosterilization of E. coli with an equivalent Hg/Ar-MDEL light source was also nearly complete (99.7%). Thus, the suitability of the environmentally friendlier Kr/Br2 gas fill to replace Hg/Ar filler gas in MDELs for the photoelimination of organic pollutants and microbial disinfection in aqueous media has been demonstrated.

Sunscreens and their usefulness: have we made any progress in the last two decades?

Sunscreens have now been around for decades to mitigate the Sun's damaging ultraviolet (UV) radiation which, although essential for the existence of life, is a recognized prime carcinogen. Accordingly, have suncreams achieved their intended purposes towards protection against sunburns, skin photo-ageing and the like? Most importantly, however, have they provided the expected protection against skin cancers that current sunscreen products claim to do? In the last two decades, there have been tens, if not hundreds of studies on sunscreens with respect to skin protection against UVB (280‒320 nm)-traditionally sunscreens with rather low sun protection factors (SPF) were intended to protect against this type of radiation-and UVA (320‒400 nm) radiation; a distinction between SPF and UVA protection factor (UVA-PF) is made. Many of the studies of the last two decades have focused on protection against the more skin-penetrating UVA radiation. This non-exhaustive article reviews some of the important facets of what is currently known about sunscreens with regard (i) to the physical UV filters titanium dioxide (TiO2) and zinc oxide (ZnO) and the mostly photo-unstable chemical UVB/UVA filters (e.g., octinoxate (OMC) and avobenzone (AVO), among others), (ii) to novel chemical sunscreen agents, (iii) to means that minimize the breakdown of chemical filters and improve their stability when exposed to UV sunlight, (iv) to SPF factors, and (v) to a short discussion on non-melanoma skin cancers and melanoma. Importantly, throughout the article we allude to the safety aspects of sunscreens and at the end ask the question: do active ingredients in sunscreen products pose a risk to human health, and what else can be done to enhance protection? Significant loss of skin protection from two well-known commercial suncreams when exposed to simulated UV sunlight. Cream I: titanium dioxide, ethylhexyl triazone, avobenzone, and octinoxate; Cream II: octyl salicylate, oxybenzone, avobenzone, and octinoxate.

Microwave-driven hydrogen production (MDHP) from water and activated carbons (ACs). Application to wastewaters and seawater.

This article reports on low-temperature steam reforming and water-gas shift processes to generate hydrogen efficiently when water is passed through microwave-heated activated carbon (AC) particulates, in contrast to conventional steam reforming that is not particularly efficient at temperatures around 600 °C. The microwave-driven method performed efficiently at this temperature producing hydrogen with yields of 70% or more, as a result of the microscopic local microwave heating of the AC particulates. To the extent that the activated carbon is produced from plant biomass-related raw materials, the carbon dioxide produced is carbon neutral. Conditions for hydrogen generation were optimized with regard to the size of the AC particles, the water flow rate, and the size of the reactor. For practical applications of this microwave-based method, hydrogen was also generated efficiently with yields of 75-80% when using spent activated carbons (large size distribution) and model contaminated wastewaters and artificial seawater; significant energy was saved under the conditions used. The re-use of spent ACs eliminates the need for their disposal after being used in water and sewage treatments. In addition, the presence of any organic matter in wastewaters is also a likely effective source of hydrogen (yields, 75-85%). And not least, although generation of hydrogen from seawater is a difficult electrolytic process, the microwave method proved to be an attractive and efficient technology toward hydrogen generation from seawater with yields of 85 to 90%. Addition of Pt deposits on the activated carbon support, however, provided no advantages over pristine AC particulates.

A novel green chemistry gelation method for polyvinyl pyrrolidone (PVP) and dimethylpolysiloxane (silicone): microwave-induced in-liquid-plasma.

The focus of this article rests on our discovery that a water-soluble polymer could be cross-linked to form a gel using a novel Green Chemistry gelation method: the microwave-induced in-liquid-plasma (MILP) method that requires neither a cross-linking agent nor an initiator as are required in the conventional chemical method. For instance, the water-soluble polyvinyl pyrrolidone (PVP) polymer was gelled by MILP plasma irradiation within a few minutes without using toxic cross-linking agents and initiators. As well, the hydrophobic dimethylpolysiloxane macromolecule was dispersed in aqueous media to a colloidal sol, which could then also be easily gelled under MILP irradiation conditions within a few minutes, in comparison to the conventional method that often requires several hours to days for gelation to occur in the presence of cross-linking agents and initiators. The viscosity of the MILP silicone gel was greater than a similar gel formed by the conventional method. In contrast, the viscosity of the MILP-formed PVP gel was lower than the viscosity of the PVP gel obtained from the conventional method. Gels were characterized by 13C-NMR spectrometry, FT-IR spectroscopy, SEM microscopy, viscosity measurements, and dynamic light scattering for particle size distributions. Plausible mechanistic stages for the two gelation occurrences have been inferred as involving the synergistic effects from microwaves, together with the sound waves (cavitation microbubbles), heat, UV and ˙OH radicals resulting from the microwave-generated in-liquid-plasma.

Enhanced Degradation of Organic Pollutants with Microwave-induced Plasma-in-liquid (MPL): Case of Flame Retardant Tetrabromobisphenol-A in Alkaline Aqueous Media.

We report the enhanced degradation of a widely used brominated flame retardant, tetrabromobisphenol-A (TBBPA), which is soluble only in organic solvents and strongly alkaline solutions, where most advanced oxidation processes (AOPs) for such substrates tend to be rather inefficient. We further report an environmentally friendly method (microwave-induced plasma-in-liquid; MPL) that operates efficiently in alkaline aqueous media without the need for organic solvents to enhance the solubility of TBBPA in water. The enhanced debromination and almost complete mineralization of TBBPA under alkaline conditions occurs within 20 min of MPL irradiation. This method, which is a new member of the AOP family, provides a simple and green approach to detoxify aqueous media contaminated with TBBPA, which requires only electric power and neither catalysts nor oxidizing agents. Several intermediate species have been identified by liquid chromatography/mass spectrometry (LC-MS), following events that involved reactive oxygen species (ROSs) such as·OH, whose first task was to approach the substrate at carbon atoms bearing the highest electron densities.

Microwave-/UV-assisted Enhancement of the Wettability of Photoactive TiO2 Substrates Coated on an Inactive Ti/i-TiO2 Base.

Titanium dioxide (TiO2) has been proven to be an excellent system for wettability patterning purposes because of its super hydrophilic ability and its oxidative/reductive degradation of substances when exposed to UV radiation. TiO2 substrates upon which was deposited a self-assembled monolayer (SAM) of n-octadecyltrimethoxysilane (ODS) shifts the surface to become super hydrophobic, which when subjected to UV irradiation causes the ODS compound to be degraded with the substrate turning back to be super hydrophilic. Such events allow wettability patterns to be easily created. The objective of this study was to reduce the time required to construct a wettability pattern. For this purpose, highly photoactive TiO2 nanoparticles were coated onto a titanium plate whose surface had been previously oxidized at high temperatures in an electric furnace. The subsequent TiO2/Ti system was microwaved and simultaneously irradiated with ultraviolet light (UV) to further accelerate its photocatalytic activity. Using a set of photomasks and both UV and microwave irradiation, the generation of a pattern was achieved 15 times faster (2 min versus 30 min) compared to an earlier result that used only UV radiation.

Probing the effect(s) of the microwaves' electromagnetic fields in enzymatic reactions.

This paper examines the effects that electromagnetic fields from microwave radiation have in enzymatic reactions. Hydrolysis of proteins in beef (in vivo case) and casein (in vitro case) by the papain enzyme, a major industrial enzyme, is used herein as a model reaction to assess, under highly controlled conditions, the various parameters of microwave radiation (electric field, magnetic field, pulsed microwave irradiation, continuous microwave irradiation) as they might influence these in vivo and in vitro enzymatic reactions. The effect(s) of the microwaves' electromagnetic fields was clearly evidenced in the in vivo case, contrary to the in vitro case where no such effect was observed, likely due to the nature of the hydrolysis reaction and to the autolysis (self-digestion) of the papain enzyme. Additionally, the effect of pulsed versus continuous microwave irradiation was further assessed by examining the catalase-assisted decomposition of hydrogen peroxide.

Development of a Hg-free UV light source and its performance in photolytic and photocatalytic applications.

Constraints on light sources that use mercury (arc lamps) are evolving with the establishment of the Minamata Convention, which has led to the proliferation of LEDs. However, no LED light source emits intense ultraviolet radiation at wavelengths below 300 nm for photolytic applications. Thus, it is necessary to develop suitable UV light sources for the decontamination of wastewater and water sterilization processing. Herein, we explore various substitute gases (e.g., N2, Ar, He and SF6) to replace mercury, which is commonly employed in arc lamps, using an EL (electroluminescence) quartz assembly platform similar to microwave-discharge electrodeless lamps. Although nitrogen is an inexpensive and safe gas, it cannot generate significant UV radiation in the UVC region of 200-300 nm. This problem in the Hg-free light source was resolved by mixing a very small quantity of sulfur hexafluoride (SF6) as an additive filler gas in a nitrogen-, argon- or helium-filled assembly. The low-pressure mercury lamp consisting of Hg/Ar filler gases is ca. 25% more efficient than the novel N2/SF6 lamp toward the photolytic decomposition of Rhodamine-B (RhB) dye-contaminated wastewater (1.66 × 10-4 mM min-1versus 1.22 × 10-4 mM min-1). Nonetheless, the latter has proven far more efficient than an LED source emitting 365 nm radiation (0.057 × 10-4 mM min-1). The addition of TiO2 to RhB-contaminated wastewater demonstrated that this Hg-free N2/SF6 light source is as efficient as the corresponding Hg/Ar electroluminescent lamp toward the photocatalytic decomposition of the RhB dye pollutant.

Microwave Flow Chemistry as a Methodology in Organic Syntheses, Enzymatic Reactions, and Nanoparticle Syntheses.

Several studies have used microwaves as a heat source for carrying out various types of reactions employing circulation reaction vessels. The microwave flow chemical synthesis methodology is most appropriate in the use of microwaves in chemical syntheses. It can attenuate the problem of microwave heating (non-uniform heating and penetration depth) and maximize the benefits (rapid heating and first temperature adjustments). In this brief review, we examine and explain some of the relevant features of microwave heating with applicative examples of the usage of microwave flow chemistry equipment in carrying out organic syntheses, enzymatic reactions, and (not least) nanoparticle syntheses.

The electromagnetic wave energy effect(s) in microwave-assisted organic syntheses (MAOS).

Organic reactions driven by microwaves have been subjected for several years to some enigmatic phenomenon referred to as the microwave effect, an effect often mentioned in microwave chemistry but seldom understood. We identify this microwave effect as an electromagnetic wave effect that influences many chemical reactions. In this article, we demonstrate its existence using three different types of microwave generators with dissimilar oscillation characteristics. We show that this effect is operative in photocatalyzed TiO2 reactions; it negatively influences electro-conductive catalyzed reactions, and yet has but a negligible effect on organic syntheses. The relationship between this electromagnetic wave effect and chemical reactions is elucidated from such energetic considerations as the photon energy and the reactions' activation energies.

Water Will Be the Coal of the Future-The Untamed Dream of Jules Verne for a Solar Fuel.

This article evokes the futuristic visions of two giants, one a writer, Jules Verne, who foresaw water as the coal of the future, and the other a scientist, Giacomo Ciamician, who foresaw the utilization of solar energy as an energy source with which to drive photochemical and photocatalytic reactions for the betterment of mankind. Specifically, we examine briefly the early work of the 1960s and 1970s on the photosplitting of free water and water adsorbed on solid supports, based mostly on metal oxides, from which both hydrogen and oxygen evolve in the expected stoichiometric ratio of 2 to 1. The two oil crises of the 1970s (1973 and 1979) spurred the interest of researchers from various disciplines (photochemistry, photo-catalysis and photoelectrochemistry) in search of a Holy Grail photocatalyst, process, or strategy to achieve efficient water splitting so as to provide an energy source alternative to fossil fuels. Some approaches to the photosplitting of water adsorbed on solid insulators (high bandgap materials; Ebg ≥ 5 eV) and semiconductor photocatalysts (metal oxides) are described from which we deduce that metal oxides with bandgap energies around 5 eV (e.g., ZrO2) are more promising materials to achieve significant water splitting on the basis of quantum yields than narrower bandgap photocatalysts (e.g., TiO2; Ebg ≈ 3.0-3.2 eV), which tend to be relatively inactive by comparison. Although proof of concept of the photosplitting of water has been demonstrated repeatedly in the last four decades, much remains to be done to find the Holy Grail photocatalyst and/or strategy to achieve significant yields of hydrogen.

Facile preparation of N-doped TiO2 at ambient temperature and pressure under UV light with 4-nitrophenol as the nitrogen source and its photocatalytic activities.

To date syntheses of nitrogen-doped TiO2 photocatalysts (TiO2-xNx) have been carried out under high temperatures and high pressures with either NH3 or urea as the nitrogen sources. This article reports for the first time the facile preparation of N-doped TiO2 (P25 titania) in aqueous media at ambient temperature and pressure under inert conditions (Ar- and N2-purged dispersions) with 4-nitrophenol (or 4-nitrobenzaldehyde) as the nitrogen source. The resulting N-doped P25 TiO2 materials were characterized by UV/Vis and X-ray photoelectron spectroscopies (XPS) that confirmed the presence of nitrogen within the photocatalyst; X-ray diffraction (XRD) techniques confirmed the crystalline phases of the doped material. The photocatalytic activity of N-doped TiO2 was assessed through examining the photodegradation of 4-chlorophenol in aqueous media and iso-propanol as a volatile pollutant under UV/Vis and visible-light irradiation. Under visible light irradiation, undoped P25 was inactive contrary to N-doped P25 that successfully degraded 95% of the 4-chlorophenol (after 10 h) and 23% of iso-propanol (after 2.5 h).