Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2
TL;DR: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2 and the optimum metal content varies depending on the nature of the metal as mentioned in this paper.
Abstract: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2. The optimum metal content varies depending on the nature of the metal. A correlation between the ammonia yield and the intermediary MH bond strength is established (low bond strength gives rise to low ammonia yield).
Citations
More filters
TL;DR: In this paper, an Ag-g-C3N4/W18O49 heterojunction catalyst is prepared and used for full-spectrum-driven N2 photofixation from the UV to the NIR region for the first time.
Abstract: More than half of the solar spectrum is near infrared (NIR) light, which is seldom utilized in photocatalytic reactions. In this work, an Ag–g-C3N4/W18O49 heterojunction catalyst is prepared and used for full-spectrum-driven N2 photofixation from the UV to the NIR region for the first time. X-ray diffraction, N2 adsorption, UV-Vis-NIR spectroscopy, thermogravimetric analysis, photoluminescence, X-ray photoelectron spectroscopy and electrochemical impedance spectra were used to characterize the prepared catalysts. The result indicates that the as-prepared Ag–g-C3N4/W18O49 heterojunction catalysts display much higher N2 photofixation performance than that of individual W18O49 or Ag–g-C3N4, which should be due to the better separation rate of electron–hole pairs and more efficient light utilization. g-C3N4 is the active component in the catalyst for N2 photofixation. Ag loading promotes the separation rate of electron–hole pairs. W18O49 plays a role as light absorber in the full-spectrum to form more photogenerated electrons for recombining the holes in the g-C3N4 through “Z-scheme” mechanism. A possible electrons transfer route is proposed.
14 citations
TL;DR: The photocatalytic degradation of pyrene under UV irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc.
Abstract: The photocatalytic degradation of pyrene under UV (125 W Hg-Arc, 10.4 mW/cm2) irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc. As the reduction potential of these metals lies below the conduction band (CB) position (−0.1 eV) of TiO2, the photoexcited electron transfer occurs more readily and reduces electron–hole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO2 because of rapid Fermi energy equilibrium between the CB of TiO2 and its surface adsorbed metal ions. The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni2+ having more negative reduction potential (−0.25 eV) than the CB of TiO2 imparts negligible co-catalytic activity to TiO2 photoreaction. It also revealed that loading of Au3+ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe+3 and Au3+ ions gradually increases from 0.1 to 2 wt.%, the pyrene photodecomposition rate also become faster.
13 citations
Cites background from "Photocatalytic reduction of dinitro..."
...It is reported (Kamat 2002; Ranjit et al. 1996) that depending on the work function of various metal co-catalysts, the extent of Fermi level equilibriation (Scheme 1) between metal and TiO2 governs the electron transfer ability, hence, the co-catalytic activity of metals....
[...]
...In metal–TiO2 interface, a Schottky barrier is formed between the metal and TiO2 after the migration of electrons from semiconductor to metal (Wood et al. 2001; Subramanian et al. 2004; Kamat 2002; Ranjit et al. 1996; Nosaka et al. 1984) as seen in Scheme 1....
[...]
TL;DR: Aperiodic mesoporous TiO2-SiO2 mixed oxide materials were platinized by the incorporation of Pt0 by three different methods to understand the role of Pt on the photocatalytic activity of phenol under solar simulated conditions as discussed by the authors.
Abstract: Aperiodic mesoporous TiO2–SiO2 mixed oxide materials were platinized by the incorporation of Pt0 by three different methods to understand the role of Pt on the photocatalytic activity of phenol under solar simulated conditions. The physicochemical properties of the resultant photocatalysts were examined by powder X-ray diffractometry, nitrogen adsorption, diffuse reflectance spectroscopy, and transmission electron microscopy. These characterization techniques illustrated the enhanced morphological properties of the mesostructure such as the presence of highly crystalline anatase TiO2, large pore geometries, and active Ti–O–Si linkages, respectively. CO chemisorption analysis and TEM images accentuated the role of small Pt crystallite sizes in the development of photocatalysts with high degradation efficiencies.
13 citations
31 Jul 2019
TL;DR: A series of Mn2xIn2(1-x)S3 (x < 0.5) nanoflower solid solutions (NSS) were synthesized by a simple one-step hydrothermal method using l-cysteine as S source and chelating reagent as discussed by the authors.
Abstract: A series of Mn2xIn2(1–x)S3 (x < 0.5) nanoflower solid solutions (NSS) were synthesized by a simple one-step hydrothermal method using l-cysteine as S source and chelating reagent. The Mn2xIn2(1–x)S...
12 citations
TL;DR: The obtained results confirm successful ammonia production through nitrogen splitting at room temperature and under atmospheric pressure and suggest the use of plasmonic aluminium structures remarkably improves the ammonia production rate.
Abstract: Ammonia production at room temperature and atmospheric pressure is in high demand to assist in energy saving and the protection of the environment worldwide, as well as to help reduce CO2 emissions. Recently, plasmonic nanomaterials have been frequently used for solar to chemical energy conversion, which has the potential to replace existing energy-intensive industrial processes. In our approach, plasmonic aluminium nanotriangles (AlNTs) were used to investigate the impact of plasmonic effects on photocatalytic ammonia production. Plasmonic near-field coupling to a semiconductor and hot electron generation from AlNTs were studied in detail through the use of electrochemical photocurrent measurements. A narrowband LED beam with a central wavelength at 365 nm was used to illuminate the AlNTs and their hot electron generation efficiency was estimated to be 2 × 10−4%, resulting in an ammonia production rate of 4 × 10−5 μM h−1 mW−1 cm−2, which corresponds to a quantum efficiency of 2.5 × 10−5%. In the case of plasmonic near-field coupling, AlNTs-embedded TiO2 demonstrates a charge-carrier generation efficiency of 2.7%, which is ∼2.3 times higher than that of bare TiO2. The ammonia production rate of AlNTs–TiO2 is 0.1 μM h−1 mW−1 cm−2 with a quantum efficiency of ∼0.06%, which corresponds to ∼2.4 times that of the rate demonstrated by bare TiO2 (0.04 μM h−1 mW−1 cm−2, quantum efficiency ∼ 0.025%). The obtained results confirm successful ammonia production through nitrogen splitting at room temperature and under atmospheric pressure. Moreover, according to the presented results, the use of plasmonic aluminium structures remarkably improves the ammonia production rate.
12 citations
References
More filters
TL;DR: In this paper, the dependence of the exchange current for the electrolytic evolution of hydrogen on metals (i 0,H ) on the work function is analyzed on the basic of a new list of polycrystalline surfaces.
1,474 citations
TL;DR: The photolysis of chemisorbed water on incompletely outgassed TiO/sub 2/ powder yields H 2 and O 2 in the molar ratio of 2 : 1 if conducted under argon in the presence of molecular nitrogen as mentioned in this paper.
Abstract: The photolysis of chemisorbed water on incompletely outgassed TiO/sub 2/ powder yields H/sub 2/ and O/sub 2/ in the molar ratio of 2 : 1 if conducted under argon In the presence of molecular nitrogen, O/sub 2/ is still formed but the evolution of H/sub 2/ is inhibited as chemisorbed nitrogen is reduced to NH/sub 3/ and traces of N/sub 2/H/sub 4/ according to N/sub 2/ + 3H/sub 2/O + nhv yields 2NH/sub 3/ + 150/sub 2/ and N/sub 2/ + 2H/sub 2/O + mhv yields N/sub 2/H/sub 4/ + O/sub 2/ Iron doping enhances the photocatalytic reactivity of rutile and provides prototypes of solar cells for photochemical ammonia synthesis from N/sub 2/ and H/sub 2/O
817 citations
TL;DR: In this article, the improvement of H/sub 2/ evolution from two different types of catalytic p-type photocathode surfaces has been examined, and a comparison of the naked p-Si, the simply platinized, and the (PQ/sup 2 +//sup ///sup +/.)sub n/.nPt(0))/sub surf/ system compared to the same surface directly platinised confirm an important difference in the mechanism of H /sub 2 / evolution catalysis for the two surface catalyst systems.
Abstract: The improvement of H/sub 2/ evolution from two different types of catalytic p-type photocathode surfaces has been examined. p-Type Si has been platinized by phtotelectrochemically plating Pt(0) onto the Si surface. Such a photocathode shows significant improvement (compared to naked p-type Si) for photochemical H/sub 2/ evolution with respect to output photovoltage, fill factor, and overall efficiency. Such photocathodes having an optimun amount of Pt(0) give a pH-dependent output voltage with respect to the H/sub 2/O/H/sub 2/ couple, but the dependence is not a simple 59-mV/pH dependence. No pH dependence would be expected if Pt(0) formed a Schottky barrier when plated onto p-type Si. A second kind of H/sub 2/ evolution catalyst has been confined to the surface of p-type Si. Polymeric quantities of an electroactive N,N'-dialkyl-4,4'-bipridinium reagent, (PQ/sup 2 +/.)/sub n/, have been confined to the surface. The Br/sup -/ counterions of the polymer are then exchanged by PtCl/sub 6//sup 2 -/. Photoreduction then yields Pt(0) dispersed in the polymer. Such a surface is again significantly improved compared to naked p-type Si with respect to H/sub 2/ evolution. A comparison of the naked p-Si, the simply platinized, and the (PQ/sup 2 +//sup ///sup +//sub n/.nPt(0))/sub surf./ system is mademore » and contrasted to the expected behavior of an external Schottky barrier photocell driving an electrolysis cell with a Pt cathode. Experiments with n-type MoS/sub 2/, n-type Si, Pt, Au, and W cathodes functionalized with the (PQ/sup 2 +//sup ///sup +/.)sub n/.nPt(0))/sub surf./ system compared to the same surface directly platinized confirm an important difference in the mechanism of H/sub 2/ evolution catalysis for the two surface catalyst systems. p-Type Si modified with optimum amounts of Pt(0) by direct platinization appears to give improved H/sub 2/ evolution efficiency by a mechanism where the Pt(0) serves as a catalyst that does not alter the interface energetics of the semiconductor.« less
318 citations
TL;DR: The quantum yield of hydrogen production was increased greatly by supporting metals or metal complexes on the TiO2 surface, amounting to 38% for a Pt-TiO2 photocatalyst.
218 citations
TL;DR: In this paper, the Fermi level difference of p-InP and H/sup +//H/sub 2/ (0.9 +/- 0.2 eV) was shown to be a function of metal work functions.
Abstract: Noble metal incorporation in the surface of p-type semiconductor photocathodes to catalyze hydrogen evolution leads to efficient solar to chemical conversion if a set of energetic and kinetic criteria are satisfied: (1) the semiconductor-catalyst junction barrier height must be equal to or greater than that of the semiconductor H/sup +//H/sub 2/ junction; (2) the recombination velocity of photogenerated electrons at the semiconductor-catalyst interface must be low; (3) the overpotential for hydrogen evolution at solar cell current densities (approx.30 mA/cm/sup 2/) must be minor. Because of substantial differences in the vacuum work functions of Pt, Rh, Ru, and the (redox potential of the) H/sup +//H/sub 2/ couple, the barrier heights for junctions of each of the four systems with p-InP ought to vary widely. Yet experiments show that all p-InP(M)/H/sup +//H/sub 2/ junctions, where M = Pt, Rh, Ru, or no metal, have essentially the same approx.0.7-V gain in onset potential for hydrogen evolution relative to Pt/H/sup +//H/sub 2/. We attribute the similarity to the known lowering of metal work functions upon hydrogen alloying. Such alloying increases the barrier height and thereby the gain in onset potential over that anticipated from the vacuum work functions. The barrier height, measured as themore » limiting value of onset potential gain at high irradiance, approaches in all cases the Fermi level difference of p-InP and H/sup +//H/sub 2/ (0.9 +/- 0.2 eV). That Fermi level pinning by interfacial states is not the cause of the similar barriers is evident from the reversible decrease in onset potential with hydrogen depletion and by a unity diode perfection factor of the p-InP(Rh)/H/sup +//H/sub 2/ photocathode, which indicates no measurable interfacial recombination of photogenerated carriers. In agreement, the quantum efficiency of carrier collection (hydrogen evolution) nears unity.« less
184 citations