Light-activated Catalyst Research Articles

Solar light-driven photocatalysis by Co doped SnS nanoparticles towards degradation of noxious organic pollutant: Mechanism and toxicity assessment

Tin Sulphide (SnS), one of the main sulfide compounds, has generated a great deal of interest because of its distinctive properties and diverse applications. Pure and Cobalt (Co) doped tin Sulphide (SnS) nanoparticles (NPs) have been synthesized by a facile co-precipitation approach. The synthesized nanoparticles were characterized using various characterization techniques such as X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), Raman, UV-Vis Spectroscopy, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) studies were used to investigate and confirmed the crystalline, optical, and morphological features of nanoparticles. Under the irradiation of natural sunlight, the synthesised nanoparticles effectively performed as a visible light-activated catalyst for the degradation of Crystal violet (CV) and Bromophenol blue (BP) dyes. A 7% of Co-doped SnS catalyst showed excellent photodegradation efficiency of 95.5% and 93.0% for CV and BP, respectively. Rate constant values of 0.066 and 0.059 min−1 are estimated for CV and BP degradation, respectively. The higher photocatalytic activity might be attributed to Co doping, with the doped Co then playing a substantial role in lowering bandgap and boosting charge carriers, superoxide radical, and hydroxyl radical production, which prevents recombination and thus improves the efficiency and stability of the photocatalyst. Additionally, the toxicity of Vigna radiata seeds that are readily available commercially is evaluated using the treated, untreated dye solution, and control solutions.

Light-activated catalyst makes syngas greener

Synthesis gas, or syngas, is a feedstock for multiple industrial processes, including the Haber-Bosch process for making ammonia. Syngas is a mixture of carbon monoxide, carbon dioxide, and hydrogen. Gasification plants, which make syngas from coal, natural gas, and other sources, use catalysts to break apart fuels at around 800 °C. Naomi Halas and coworkers at Rice University have now come up with a greener way to make syngas (Nat. Energy 2020, DOI: 10.1038/s41560-019-0517-9). Using light to activate a nanoparticle catalyst made of copper antennas and single ruthenium atom reactor sites, the team was able to make syngas at around 200 °C. Their system is stable up to 50 h with 99% selectivity. Current industrial syngas catalysts are less robust because they’re susceptible to coking, a C–C bond-forming process that leads to the growth of a carbonaceous material that can block active sites and poison the catalyst. “By having isolated

Robust photocatalyst does double duty

Light-activated catalysts are increasingly used in reduction-oxidation reactions, generating radicals that selectively modify complex molecules. But most such photoredox catalysts rely on expensive, scarce metals like iridium and rubidium. Many are vulnerable to harsh reagents, and different reactions usually need custom catalysts. Chemists in Germany have developed an alternative that not only is cheap and stable but also can catalyze a broad range of radical-based redox reactions. The catalyst is a solid semiconductor material called mesoporous graphitic carbon nitride, an extended network of triazine-based aromatic rings that is easily prepared from cyanamide (Science 2019, DOI: 10.1126/science.aaw3254). “We believe it offers a significant improvement,” says Burkhard Konig at the University of Regensburg, part of the research team. Blue light separates charges on the catalyst’s surface, generating electrons that drive reduction reactions, and holes that handle oxidation reactions. This allows the catal...

Arylsulfonylacetamides as bifunctional reagents for alkene aminoarylation.

Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.

Arenes and amides from a single source

Organic Chemistry Pharmaceutical synthesis often requires the formation of adjacent carbon-carbon and carbon-nitrogen bonds. Monos et al. present a method that delivers the carbon and nitrogen components in a single reagent, specifically, an aryl ring tethered through sulfur dioxide to an amide. A light-activated catalyst primes an olefin to react with the nitrogen, which in turn leads to migration of the aryl ring and loss of the sulfur bridge. The efficient room-temperature process is applicable to a variety of different arenes, including heterocycles. Science , this issue p. [1369][1] [1]: /lookup/doi/10.1126/science.aat2117

Identification of few-layer ReS2 as photo-electro integrated catalyst for hydrogen evolution

Efficient water splitting via photo-electrocatalytic (PEC) systems holds great promise for producing hydrogen fuel in future energy devices. The artificial integration of photosensitive semiconductors and co-catalysts into effective PEC electrodes is becoming significantly challenging. Here, few-layer ReS2 nanosheets (NSs) were found to have both favorable solar light harvesting and proton reducing kinetics based on the assessments for electronic band structure and Gibbs free energy (ΔGH*) of hydrogen adsorption. Furthermore, the naturally coupling between optical and catalytic functions was demonstrated using ReS2 NSs grown on conductive carbon fiber clothes (CFC) as a hydrogen evolution reaction (HER) cathode, where the simulated 1 sun irradiation (100 mW cm−2) could significantly improve the catalytic activity along with anodic shifts of ca. 37 mV in onset potential and ca. 39 mV in over potential, and near 3-fold increase in exchange current density. The comparative analyses on Tafel, turnover and active sites revealed that the light-improved HER performance was due to the photo-generated hot electron injection into edge active sites. This work identifies ReS2 as a naturally PEC function-coupling material, opening a prospect of utilizing light-activated catalysts or co-catalysts to integrate catalysis with solar energy in PEC systems.

Lowering the heat for splitting nitrogen

The world relies on the Haber-Bosch process to reduce atmospheric nitrogen to ammonia to make fertilizer, pharmaceuticals, and other industrially important chemicals. But the process requires high temperature and thereby consumes a tremendous amount of energy—about 1% of the world’s electricity every year. A new light-activated catalyst could dramatically reduce the temperature needed to drive the reaction, according to computer simulations (Sci. Adv. 2017, DOI: 10.1126/sciadv.aao4710). John Mark P. Martirez and Emily A. Carter at Princeton University have proposed that a gold-molybdenum catalyst could split dinitrogen’s triple bond at room temperature using visible light. That dissociation step is the primary limit on the Haber-Bosch process’s reaction rate. Their catalyst relies on a phenomenon called surface plasmon resonance, in which the valence electrons on a nanoparticle—made of molybdenum-doped gold in this case—oscillate in unison when excited by a photon. Harnessed correctly, that excitation ene...

Potent photocatalyst for disinfecting water

A small amount of inexpensive molybdenum disulfide can function as a potent photocatalyst, killing nearly all bacteria in water samples within minutes, according to a study (Nat. Nanotechnol. 2016, DOI: 10.1038/nnano.2016.138). Using sunlight and a light-activated catalyst is a simple, low-cost way to rid water of harmful pathogens. But the process is slow, taking up to 48 hours, because typical catalysts used in this application respond primarily to ultraviolet light, which accounts for just 4% of sunlight’s energy. So Yi Cui of Stanford University and colleagues designed a catalyst that efficiently harvests visible light, which represents roughly 50% of solar energy. The team grew vertically aligned sheets of MoS2 three to 10 molecular layers thick and analyzed their properties. Exposing the catalyst in water to visible light stimulates electronic excitations that generate bacteria-killing reactive oxygen species, such as O2 •−, singlet oxygen (1O2), OH•, and hydrogen peroxide, along the edges

Precise control from a metal-free catalyst

Polymer Chemistry Polymerization can be a rather dangerous free for all, with molecules joining randomly in chains at a chaotic pace. One of modern chemistry's great accomplishments has been the development of methods to assemble polymers in steady, orderly steps. However, order comes at a price, and often it's the need for metal catalysts that are hard to remove from the plastic product. Theriot et al. used theory to guide the design of a metal-free light-activated catalyst that offers precise control in atom transfer radical polymerization, alleviating concerns about residual metal contamination (see the Perspective by Shanmugam and Boyer). Science , this issue p. [1082][1]; see also p. [1053][2] [1]: /lookup/doi/10.1126/science.aaf3935 [2]: /lookup/doi/10.1126/science.aaf7465

ChemInform Abstract: Organic Chemistry: Light Opens Pathways for Nickel Catalysis

AbstractReview: 12 refs.

Organic chemistry: Light opens pathways for nickel catalysis.

The report of a light-activated catalyst that generates usually inaccessible nickel intermediates provides a general strategy that might allow elusive catalytic reactions to be realized. See Letter p.330 Despite advances in carbon–carbon fragment couplings, the ability to create carbon–oxygen bonds via nickel catalysis has been largely unsuccessful. Here David MacMillan and colleagues show that visible-light-excited photoredox catalysts can provide transient access to Ni(III) species that readily participate in reductive elimination. Using this synergistic merger of photoredox and nickel catalysis, the authors develop a highly efficient and general carbon–oxygen coupling reaction using alcohols and aryl bromides.

A bright outlook for carbon coupling

Dual Catalysis In contemporary organic chemistry, it is straightforward to forge bonds between unsaturated carbons (i.e., carbons already engaged in double bonds) using cross-coupling catalysis. The protocol runs into some trouble, however, if one or both starting carbon centers are saturated (purely single-bonded). Tellis et al. and Zuo et al. independently found that combining a second, light-activated catalyst with a nickel cross-coupling catalyst could achieve selective coupling of saturated and unsaturated reagents (see the Perspective by Lloyd-Jones and Ball). Their methods rely on single-electron transfer from the light-activated catalyst to the saturated carbon, thereby enhancing its reactivity more effectively than the two-electron mechanisms prevailing in traditional protocols. Science , this issue p. [433][1], p. [437][2]; see also p. [381][3] [1]: /lookup/volpage/345/433?iss=6195 [2]: /lookup/volpage/345/437?iss=6195 [3]: /lookup/volpage/345/381?iss=6195

Dual catalysis. Single-electron transmetalation in organoboron cross-coupling by photoredox/nickel dual catalysis.

The routine application of C(sp3)-hybridized nucleophiles in cross-coupling reactions remains an unsolved challenge in organic chemistry. The sluggish transmetalation rates observed for the preferred organoboron reagents in such transformations are a consequence of the two-electron mechanism underlying the standard catalytic approach. We describe a mechanistically distinct single-electron transfer-based strategy for the activation of organoboron reagents toward transmetalation that exhibits complementary reactivity patterns. Application of an iridium photoredox catalyst in tandem with a nickel catalyst effects the cross-coupling of potassium alkoxyalkyl- and benzyltrifluoroborates with an array of aryl bromides under exceptionally mild conditions (visible light, ambient temperature, no strong base). The transformation has been extended to the asymmetric and stereoconvergent cross-coupling of a secondary benzyltrifluoroborate.

Pilot-Scale Demonstration of an Innovative Treatment for Vapor Emissions

ABSTRACT Researchers from the National Renewable Energy Laboratory recently conducted a pilot-scale study at McClellan Air Force Base (AFB) in Sacramento, CA. The objective of the test was to determine the effectiveness of an ambient-temperature, solar-powered photocatalytic oxidation treatment unit for destroying emissions of chlorinated organic compounds from an air stripper. This paper reports test results and discusses applications and limitations of the technology. A 10-standard-cubic-foot-per-minute (SCFM) (28.3 L/min) slip stream of air from an air stripper at Operative Unit 29-31 at McClellan AFB was passed through a reactor that contained a lightweight, perforated, inert support coated with photoactive titanium dioxide. The reactor faced south and was tilted at a 45° angle from vertical so that the light-activated catalyst received most of the available sunlight. An online portable gas chro-matograph with two identical columns simultaneously analyzed the volatile organic compounds contained in the reactor inlet and outlet air streams. Summa canister grab samples of the inlet and outlet were also collected and sent to a certified laboratory for U.S. Environmental Protection Agency Method TO-14 analysis and verification of our field analyses. Three weeks of testing demonstrated that the treatment system's destruction and removal efficiencies (DREs) are greater than 95% at 10 SCFM with UV intensities at or greater than 1.5 milliwatts/square centimeter (mW/cm2). DREs greater than 95% at 20 SCFM were obtained under conditions where UV irradiation measured at or greater than 2 mW/cm2. In Sacramento, this provided 6 hours of operation per clear or nearly clear day in April. A solar tracking system could extend operating time. The air stream also contained trace amounts of benzene. We observed no loss of system performance during testing.