Photocatalytically Active Graphitic Carbon Nitride as an Effective and Safe 2D Material for In Vitro and In Vivo Photodynamic Therapy.

Thanks to its photocatalytic property, graphitic carbon nitride (g-C3 N4 ) is a promising candidate in various applications including nanomedicine. However, studies focusing on the suitability of g-C3 N4 for cancer therapy are very limited and possible underlying molecular mechanisms are unknown. Here, it is demonstrated that photoexcitation of g-C3 N4 can be used effectively in photodynamic therapy, without using any other carrier or additional photosensitizer. Upon light exposure, g-C3 N4 treatment kills cancer cells, without the need of any other nanosystem or chemotherapeutic drug. The material is efficiently taken up by tumor cells in vitro. The transcriptome and proteome of g-C3 N4 and light treated cells show activation in pathways related to both oxidative stress, cell death, and apoptosis which strongly suggests that only when combined with light exposure, g-C3 N4 is able to kill cancer cells. Systemic administration of the mesoporous form results in elimination from urinary bladder without any systemic toxicity. Administration of the material significantly decreases tumor volume when combined with local light treatment. This study paves the way for the future use of not only g-C3 N4 but also other 2D nanomaterials in cancer therapy.

The Effect of Materials Architecture in TiO2 /MOF Composites on CO2 Photoreduction and Charge Transfer.

CO2 photoreduction to C1 /C1+ energized molecules is a key reaction of solar fuel technologies. Building heterojunctions can enhance photocatalysts performance, by facilitating charge transfer between two heterojunction phases. The material parameters that control this charge transfer remain unclear. Here, it is hypothesized that governing factors for CO2 photoreduction in gas phase are: i) a large porosity to accumulate CO2 molecules close to catalytic sites and ii) a high number of "points of contact" between the heterojunction components to enhance charge transfer. The former requirement can be met by using porous materials; the latter requirement by controlling the morphology of the heterojunction components. Hence, composites of titanium oxide or titanate and metal-organic framework (MOF), a highly porous material, are built. TiO2 or titanate nanofibers are synthesized and MOF particles are grown on the fibers. All composites produce CO under UV-vis light, using H2 as reducing agent. They are more active than their component materials, e.g., ≈9 times more active than titanate. The controlled composites morphology is confirmed and transient absorption spectroscopy highlights charge transfer between the composite components. It is demonstrated that electrons transfer from TiO2 into the MOF, and holes from the MOF into TiO2 , as the MOF induces band bending in TiO2 .

MOF-Derived Defective Co3O4 Nanosheets in Carbon Nitride Nanocomposites for CO2 Photoreduction and H2 Production.

In photocatalysis, especially in CO2 reduction and H2 production, the development of multicomponent nanomaterials provides great opportunities to tune many critical parameters toward increased activity. This work reports the development of tunable organic/inorganic heterojunctions comprised of cobalt oxides (Co3O4) of varying morphology and modified carbon nitride (CN), targeting on optimizing their response under UV-visible irradiation. MOF structures were used as precursors for the synthesis of Co3O4. A facile solvothermal approach allowed the development of ultrathin two-dimensional (2D) Co3O4 nanosheets (Co3O4-NS). The optimized CN and Co3O4 structures were coupled forming heterojunctions, and the content of each part was optimized. Activity was significantly improved in the nanocomposites bearing Co3O4-NS compared with the corresponding bulk Co3O4/CN composites. Transient absorption spectroscopy revealed a 100-fold increase in charge carrier lifetime on Co3O4-NS sites in the composite compared with the bare Co3O4-NS. The improved photocatalytic activity in H2 production and CO2 reduction is linked with (a) the larger interface imposed from the matching 2D structure of Co3O4-NS and the planar surface of CN, (b) improvements in charge carrier lifetime, and (c) the enhanced CO2 adsorption. The study highlights the importance of MOF structures used as precursors in forming advanced materials and the stepwise functionalization of the individual parts in nanocomposites for the development of materials with superior activity.

Effect of metal ions on the indigenous radicals of humic acids: high field electron paramagnetic resonance study.

The interaction of indigenous radicals of humic acid (HA) with metal cations has been studied using high magnetic field (10.5T-285 GHz) electron paramagnetic resonance (HFEPR) spectroscopy. Strong [HA]-[metal] interaction was observed in the case of heavy metals, Cd(2+), Pb(2+), and Sr(2+), leading to formation of covalent bonds with the radicals of HA. On the contrary, alkaline earth metal ions, such as Mg(2+), generate only electrostatic interaction. The two types of indigenous radicals that exist in all HAs are influenced by the metal cations in a unified manner. This provides evidence that the two types of indigenous radicals in HAs originate from a unique, phenolic, moiety in HA. Mg(2+) ions dramatically changed the pH profile of the two radical types of HA, downshifting their interconversion pK(a) by ca. 3 pH units. This is the first experimental observation of the effect of metals on the H-dissociation of the radical centers in HAs.

Layer-by-Layer Photocatalytic Assembly for Solar Light-Activated Self-Decontaminating Textiles.

Novel photocatalytic nanomaterials that can be used to functionalize textiles, conferring to them efficient solar-light-activated properties for the decontamination of toxic and lethal agents, are described. Textiles functionalized with one-dimensional (1D) SnS2-based nanomaterials were used for photocatalytic applications for the first time. We showed that 1D SnS2/TiO2 nanocomposites can be easily and strongly affixed onto textiles using the layer-by-layer deposition method. Ultrathin SnS2 nanosheets were associated with anatase TiO2 nanofibers to form nano-heterojunctions with a tight interface, considerably increasing the photo-oxidative activity of anatase TiO2 due to the beneficial interfacial transfer of photogenerated charges and increased oxidizing power. Moreover, it is easy to process the material on a larger scale and to regenerate these functionalized textiles. Our findings may aid the development of functionalized clothing with solar light-activated photocatalytic properties that provide a high level of protection against chemical warfare agents.

Single-Step Synthesis of SnS2 Nanosheet-Decorated TiO2 Anatase Nanofibers as Efficient Photocatalysts for the Degradation of Gas-Phase Diethylsulfide.

We report on a facile one-step soft hydrothermal process for synthesizing 1D anatase TiO2 nanofibers decorated with ultrathin SnS2 nanosheets. H-titanate nanofibers were used as preshaped Ti precursor. Under controlled conditions, the H-titanate structure was transformed into anatase maintaining the fibril morphology, while at the same time SnS2 nanosheets were grown in situ on the surface of the nanofibers. The successful formation of SnS2 nanosheets on the TiO2 nanofibers was confirmed by high-resolution TEM, and together with XPS spectroscopy, the tight interface formed between the SnS2 and the anatase TiO2 nanofibers was verified. The 1D SnS2/TiO2 hierarchical nanostructures with semiconductor heterojunction were proven to be very efficient under artificial solar irradiation in the photocatalytic degradation of gaseous diethylsulfide as simulant for live yperite chemical warfare agent as well as model substrate for malodorous organosulfide volatile organic compounds. SnS2 did not operate as a visible light sensitizer for TiO2 but rather as an oxidizing agent and charge-carrier separator. The semiconductor ratio in the heterostructure controlled the photoactivity. Samples with no or high content of SnS2 were less active than those with moderate SnS2 content. Enhanced reactivity was ascribed to an efficient separation of the photogenerated charge carriers driven by the differences in band edge positions and favored by the tight interface within the coupled heterostructure.

High-field 285 GHz electron paramagnetic resonance study of indigenous radicals of humic acids.

Humic substances, the largest source of carbon on Earth, contain indigenous stable free radicals that are involved in important biogeochemical environmental processes occurring in soil and water systems. Here, we present the first high-magnetic-field 285GHz electron paramagnetic resonance spectra for humic acids from various geographical origins. All humic acids irrespective of their origin contain two limiting types of indigenous stable radicals, types I and II, with distinct electronic structure. Type I, which prevails at acidic pH 5, is characterized by a g tensor with principal values gIx = 2.0032, gIy = 2.0032, and gIz = 2.0023. Type II, which prevails at alkaline pH 12, is characterized by gIIx = 2.0057, gIIy = 2.0055, and gIIz = 2.0023. The two limiting types are correlated in a unified reversible manner with pH, irrespective of the geographic origin of the HA. Both types of radical centers are consistent with pi-type radicals. They persist not only in liquid solutions but also in humic acid powders.

Structure-catalytic function relationship of SiO2-immobilized mononuclear Cu complexes: an EPR study.

Mononuclear CuL and Cu(2L) complexes, where L is propyl-thiazol-2-ylmethylene-amine, covalently immobilized onto SiO2, can catalyze efficiently the oxidation of 3,5-di-t-butylcatechol (DTBC) to 3,5-di-t-butylquinone (DTBQ) by utilizing ambient O2 as oxidant. By increasing the loading of L on SiO2, the DTBQ formation can be improved up to 400% vs the homogeneous catalyst. Equally important is however that grafting per se at low loading is not adequate for an improved catalytic activity. Appropriate loadings have to be achieved, which then may result in significant catalytic performance. Based on EPR spectroscopy a theoretical method is developed, eq A12, for spin-spin distance estimation in heterogeneously dispersed surface complexes. Practical rules including error estimates are provided. By applying this method to the [SiO2-CuL] catalysts it is shown that mononuclear copper complexes fixed on SiO2 with Cu...Cu distances as short as 4.9 +/- 0.3 A are responsible for the improved catalytic activity. The present results demonstrate that mononuclear Cu complexes can have considerable catecholase activity, if the proper geometrical proximity can be fixed. Grafting on SiO2 may be an efficient method for engineering catalysts with improved performance.

Effects of dissolved carboxylates and carbonates on the adsorption properties of thiuram disulfate pesticides.

The adsorption of thiram and disulfiram onto alpha-Al2O3 and montmorillonite clay has been studied in the presence of small carboxylate anions, bicarbonate, formate, and oxalate. At natural concentrations, HCO3- enhances dramatically the adsorption of both pesticides on alpha-Al2O3 and clay. An analogous significant enhancement of pesticide adsorption is also observed in the presence of formate and oxalate. Density functional theory calculations demonstrate that in solution a stable molecular complex between one molecule of thiram and one molecule of HCO3- is formed with interaction energy -35.6 kcal/mol. In addition, two H20 molecules further stabilize it by an interaction energy of -3.6 kcal/mol. This clustering [thiram- HCO3- -2H2O] leads to a change of the electronic structure and the ultraviolet-visible spectrum of thiram that is observed experimentally. Surface complexation modeling shows that the molecular cluster [thiram-HCO3- -2H2O], which bears a total net charge of -1, is responsible for the observed enhanced adsorption on the charged surface of alumina and clay at pH below their points of zero surface charge. The results reveal a novel pervasive role of carboxylate anions and particularly HCO3- on the adsorption of dithiocarbamate pesticides in natural waters.