In situ preparation of few-layered WS₂ nanosheets and exfoliation into bilayers on CdS nanorods for ultrafast charge carrier migrations toward enhanced photocatalytic hydrogen production

Gopannagari, Madhusudana,Kumar, D. Praveen,Reddy, D. Amaranatha,Hong, Sangyeob,Song, Myeong In,Kim, Tae Kyu Elsevier 2017 Journal of catalysis Vol.351 No.-

<P><B>Abstract</B></P> <P>Transition-metal dichalcogenides (TMD) have emerged as a fascinating new class of noble-metal-free materials for photocatalytic hydrogen evolution from the water. Recently, numerous approaches have been established to develop single- or few-layered TMDs to improve their physical properties. Although WS<SUB>2</SUB> has a higher intrinsic electric conductivity than the MoS<SUB>2</SUB> analogue, most photocatalytic studies using TMD have focused on the nanocomposite using MoS<SUB>2</SUB> as a co-catalyst. In the present study, we synthesized in situ and highly efficient few-layered WS<SUB>2</SUB> nanosheets and exfoliated them to bilayers (i.e., ultrathin) on CdS nanorods (UWC) by a simple ultrasonication process. The optimized UWC-6 photocatalyst exhibits a tremendous rate of H<SUB>2</SUB> production of ∼185.79mmolh<SUP>−1</SUP> g<SUP>−1</SUP> using simulated solar light irradiation, with a quantum efficiency of 40.5%. The performance of this photocatalyst is 33 times greater than that of pristine CdS and 3.5-fold greater than that of few-layered WS<SUB>2</SUB>–CdS nanocomposite (BWC) photocatalysts. The ultrathin WS<SUB>2</SUB> nanosheets are long and discontinuously stacked along the CdS nanorods, with high coverage of mixed-phase layers. This combination leads to the efficient photogeneration of charge carriers and enhances the surface shuttling properties of the photocatalyst for greater effective H<SUB>2</SUB> production via active edge sites and superior intrinsic electrical conductivity. The H<SUB>2</SUB> evolution rate reported here is much higher than for bulk or few-layered WS<SUB>2</SUB>-assisted CdS photocatalysts. To the best of our knowledge, this is the highest H<SUB>2</SUB> production rate achieved by a WS<SUB>2</SUB>-based CdS photocatalyst by splitting water using simulated solar light irradiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of few-layered WS<SUB>2</SUB> and exfoliation into bilayers on 1D CdS nanorods. </LI> <LI> The WS<SUB>2</SUB> existed with mixed phases (metallic 1T and semiconducting 2H) on 1D CdS. </LI> <LI> A highly stable rate of H<SUB>2</SUB> evolution ∼185.79mmolh<SUP>−1</SUP> g<SUP>−1</SUP> with 40.5% QE was observed. </LI> <LI> Rate of H<SUB>2</SUB> evolution is much higher than for few-layered WS<SUB>2</SUB>/CdS and their individuals. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of surface-functionalized multi-walled carbon nanotubes on CdS nanohybrids for effective photocatalytic hydrogen production

Gopannagari, Madhusudana,Kumar, D. Praveen,Park, Hanbit,Kim, Eun Hwa,Bhavani, Palagiri,Reddy, D. Amaranatha,Kim, Tae Kyu Elsevier 2018 Applied Catalysis B Vol.236 No.-

<P><B>Abstract</B></P> <P>Carbon nanotubes (CNTs) have enormous potential for application due to their extreme hydrophobicity. Further, their physico-chemical properties can be modified by surface functionalization. Acid functionalization of CNTs is one of the basic methodology for modification of their electro-chemical properties, resolving the poor dispersion capability, and improving the surface-active sites to enhance the photocatalytic efficiency. However, the role of surface functional groups on CNTs for water-splitting in association with CdS photocatalysts has not yet been sufficiently explored. Hence, in the present study, we report the influence of surface-functionalized CNT-metal nanoparticle (NP) hybrids attached to CdS nanorods for enhanced photocatalytic H<SUB>2</SUB> production. Significant improvement in photocatalytic H<SUB>2</SUB> production was observed for binary composites such as amine (Nf-), sulfonic (Sf-), and ascorbic acid (Af-) functionalized CNTs and CdS nanorods. Furthermore, the secondary functionalized Af-CNTs were incorporated with metal NPs and the photocatalytic activity was significantly improved in ternary metal-Af-CNT/CdS nanohybrids. Among the metal NPs, Pt- incorporated into Af-CNTs and its CdS nanohybrid led to the highest rate of H<SUB>2</SUB> production (120.1 mmol h<SUP>−1</SUP> g<SUP>−1</SUP>), corresponding to a 48-fold enhancement relative to that of pure CdS. The enhanced rate of H<SUB>2</SUB> production is attributed to the influence of the surface functional groups on the CNTs. The intimate interfacial contact between CdS, functionalized CNTs and metal NPs leads to enhanced photocatalytic performance, as a contributing factor for improving photogenerated charge separation and transportation. Moreover, the functional groups on CNTs (Pt-Af-CNT/CdS) led to obvious advantages, such as enhanced photoactivity and photostability of CdS for H<SUB>2</SUB> production. The photocatalytic performance of these nanohybrids was found to be highly influenced by the surface states of the CNTs, suggesting the importance of surface treatment of materials for H<SUB>2</SUB> evolution.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Multi-functional role of Af-CNTs observed in between CdS and metal nanoparticles. </LI> <LI> Effect of secondary surface functionalized CNTs on CdS for water-splitting reaction. </LI> <LI> Intimate interfacial contacts in CdS, fCNTs and metal NPs led effective performance. </LI> <LI> High stable, utmost rate of H2 i.e., 120 mmol h<SUP>−1</SUP> g<SUP>−1</SUP> with 29.1% QE was observed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This work demonstrates a novel approach of employing the ascorbic acid secondary functionalized CNTs leads to the dual role of a supporting semiconductor photocatalyst and metal co-catalyst, and assists with catalyzing proton/water reduction in water splitting reactions.</P> <P>[DISPLAY OMISSION]</P>

Designing CdS Mesoporous Networks on Co-C@Co₉ S₈ Double-Shelled Nanocages as Redox-Mediator-Free Z-Scheme Photocatalyst

Reddy, D. Amaranatha,Park, Hanbit,Gopannagari, Madhusudana,Kim, Eun Hwa,Lee, Seunghee,Kumar, D. Praveen,Kim, Tae Kyu Wiley (John WileySons) 2018 ChemSusChem Vol.11 No.1

<P>Designing porous nanostructures with unprecedented functionalities and an effective ability to harvest the maximum energy region of the solar spectrum and suppress the charge-carrier recombination rate offers promising potential for sustainable energy production. Although several functional porous nanostructures have been developed, high-efficiency materials are still needed. Herein, we report a new, highly active, noble-metal-free, and redox-mediator-free Z-scheme photocatalyst, CdS/Co-C@Co9S8, for H-2 production through water splitting under solar irradiation. The designed photocatalytic system contains open 3D CdS mesopores as a light absorber for wider solar-light harvesting. Metal-organicframework-derived cobalt nanocrystal-embedded few-layered carbon@Co9S8 double-shelled nanocages were used as a co-semiconductor to hamper the photo charge-carrier recombination by accelerating the photogenerated electrons and holes from the other semiconductor. The optimized catalyst shows a H-2 evolution rate of 26.69mmolg(-1)h(-1) under simulated solar irradiation, which is 46times higher than that of the as-synthesized CdS mesoporous nanostructures. The apparent quantum yield reached 7.82% at =425nm in 5h. The outstanding photocatalytic activity of CdS/Co-C@Co9S8 reflects the favorable suppression of the charge-carrier recombination rate, as determined by photoluminescence, photocurrent, and impedance analyses. We believe that the findings reported here may inspire the design of new noble-metal-free porous nanohybrids for sustainable H-2 production.</P>

Highly efficient hydrogen generation in water using 1D CdS nanorods integrated with 2D SnS₂ nanosheets under solar light irradiation

Rangappa, A. Putta,Kumar, D. Praveen,Gopannagari, Madhusudana,Reddy, D. Amaranatha,Hong, Yul,Kim, Yujin,Kim, Tae Kyu Elsevier 2020 APPLIED SURFACE SCIENCE - Vol.508 No.-

<P><B>Abstract</B></P> <P>The development of low-cost and noble-metal-free catalysts for the photoconversion of water into hydrogen (H<SUB>2</SUB>) is of great interest. Here, 2D tin(IV) sulfide (SnS<SUB>2</SUB>) ultrathin nanosheets as co‐catalysts are coupled with 1D cadmium sulfide (CdS) nanorods for the photosplitting of water into H<SUB>2</SUB>. The design of the catalyst can facilitate the passivation of the physiochemical properties of CdS and enhance H<SUB>2</SUB> evolution activity. The prepared CdS/SnS<SUB>2</SUB> composite catalyst increases the H<SUB>2</SUB> generation activity and exhibits excellent and continuous long-term photostability. The H<SUB>2</SUB> evolution rate of the optimized CdS/SnS<SUB>2</SUB> composite is approximately 9-fold that of pristine CdS nanorods. The characterization results of the CdS/SnS<SUB>2</SUB> composite reveal that the loading of SnS<SUB>2</SUB> can enhance the synergistic effects of the photocatalyst due to the effective separation, large number of exposed catalytic sites, and highly dispersed nature of the layered SnS<SUB>2</SUB>. Several characterization outcomes of CdS/SnS<SUB>2</SUB> are examined in detail (e.g., structural and surface elemental results of transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy). Further, the optoelectrical properties and charge-carrier excitations are investigated via ultraviolet diffuse reflectance spectroscopy, photoluminescence spectroscopy, and photoelectrochemical analysis. The proposed CdS/SnS<SUB>2</SUB> composite is a promising low-cost, noble-metal-free, and high-efficiency catalyst for the photocatalytic water-reduction reaction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Superior hydrogen evolution rate which is nine folds higher than the CdS. </LI> <LI> Excellent separation of photo generated charge carriers on CdS/SnS<SUB>2</SUB> hybrid with SnS<SUB>2</SUB> insertion. </LI> <LI> Excellent photo stability (30 h) of the catalyst for long term practical applications. </LI> <LI> Uniform deposition of ultrathin SnS<SUB>2</SUB> sheets onto CdS by simple methods. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Optimal hydrogen evolution rate of 20.2 mmol h<SUP>−1</SUP> g<SUP>−1</SUP> facilitated by enhanced absorption and prolonged life time of charge carriers by SnS<SUB>2</SUB> as co-catalyst on CdS.</P> <P>[DISPLAY OMISSION]</P>

Tuning Band Alignments and Charge-Transport Properties through MoSe₂ Bridging between MoS₂ and Cadmium Sulfide for Enhanced Hydrogen Production

Kumar, D. Praveen,Kim, Eun Hwa,Park, Hanbit,Chun, So Yeon,Gopannagari, Madhusudana,Bhavani, P.,Reddy, D. Amaranatha,Song, Jae Kyu,Kim, Tae Kyu American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.31

<P>Transition-metal dichalcogenide materials play a major role in the state-of-the-art innovations for energy conversion because of potential applications resulting from their unique properties. These materials additionally show inordinate potential toward the progress of hygienic power sources to deal with increasing environmental disputes at the time of skyrocketing energy demands. Herein, we report earth-abundant, few-layered, MoSe<SUB>2</SUB>-bridged MoS<SUB>2</SUB>/cadmium sulfide (CdS) nanocomposites, which reduce photogenerated electron and hole recombination by effectively separating charge carriers to achieve a high photocatalytic efficiency. Accordingly, the MoSe<SUB>2</SUB>-bridged MoS<SUB>2</SUB>/CdS system produced effective hydrogen (193 μmol·h<SUP>-1</SUP>) as that of water using lactic acid as a hole scavenger with the irradiation of solar light. The presence of few-layered MoSe<SUB>2</SUB> bridges in MoS<SUB>2</SUB>/CdS successfully separates photogenerated charge carriers, thereby enhancing the shuttling of electrons on the surface to active edge sites. To the best of our knowledge, this few-layered MoSe<SUB>2</SUB>-bridged MoS<SUB>2</SUB>/CdS system exhibits the most effective concert among altogether-reported MoS<SUB>2</SUB>-based CdS composites. Notably, these findings with ample prospective for the development of enormously real photocatalytic systems are due to their economically viable and extraordinary efficiency.</P> [FIG OMISSION]</BR>

Earth abundant transition metal-doped few-layered MoS₂ nanosheets on CdS nanorods for ultra-efficient photocatalytic hydrogen production

Hong, Sangyeob,Kumar, D. Praveen,Kim, Eun Hwa,Park, Hanbit,Gopannagari, Madhusudana,Reddy, D. Amaranatha,Kim, Tae Kyu The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.39

<▼1><P>This work demonstrates few-layered copper doped MoS2 nanosheets used as efficient cocatalysts on CdS nanorods to achieve ultra-efficient photocatalytic production of H2 under solar light irradiation.</P></▼1><▼2><P>The development of efficient, cost-effective, clean, and renewable ways to generate hydrogen is crucial to fulfill energy demand and relieve environmental concerns. The layered nanostructures of two-dimensional transition metal dichalcogenides (TMDs) are promising non-precious and noble-metal-free materials for use as hydrogen evolution reaction photocatalysts. The activity of TMDs mainly depends on their exposed edges because the basal planes are catalytically inactive; thus, the conversion of the basal planes to catalytically active sites is a current challenge. The doping of transition metals into the MoS2 system is a fruitful way to activate the basal plane surfaces, making them catalytically active. Herein, we report few-layered copper-doped MoS2 nanosheets decorated on CdS nanorods (FCM/CdS), which are prepared by a simple method. The photocatalytic activity of the as-synthesized FCM/CdS composites was assessed by the splitting of water to generate H2 under simulated solar light irradiation in the presence of lactic acid as a hole (h<SUP>+</SUP>) scavenger. The extraordinary hydrogen production rate of 194.18 μmol h<SUP>−1</SUP>, a 52-fold enhancement compared to that of bare CdS, arises from the synergistic effect of the few-layered MoS2 and the metal doping, which leads to the effective separation of photogenerated charge carriers and improves the surface shuttling properties for efficient H2 production. The exceptional photocatalytic activity of FCM/CdS nanocomposites results from the improved edge sites, enhanced electronic conductivity, and the presence of new active sites. Furthermore, the observed H2 evolution rate was much higher than those for the individual few-layered MoS2-assisted CdS (FM/CdS) photocatalysts. The H2 production rate achieved with our MoS2-based CdS photocatalyst for water splitting under solar irradiation has been the highest observed to date. Consequently, considering the low cost and high efficiency of this system, it has enormous potential for use as a photocatalyst in various fields.</P></▼2>

Noble metal-free metal-organic framework-derived onion slice-type hollow cobalt sulfide nanostructures: Enhanced activity of CdS for improving photocatalytic hydrogen production

Kumar, D. Praveen,Park, Hanbit,Kim, Eun Hwa,Hong, Sangyeob,Gopannagari, Madhusudana,Reddy, D. Amaranatha,Kim, Tae Kyu Elsevier 2018 Applied catalysis. B, Environmental Vol.224 No.-

<P><B>Abstract</B></P> <P>The hollow materials have played a significant role in cutting-edge innovations for energy conversion due to their peculiar properties and their wide range of potential applications. These materials show great promise for the development of cleaner power sources to address growing environmental concerns at a time of increasing global demand for energy. Noble metal-free MOF-derived onion slice-type hollow structured Co<SUB>4</SUB>S<SUB>3</SUB> was developed and embedded with CdS nanoparticles for photocatalytic hydrogen production. The incorporation of Co<SUB>4</SUB>S<SUB>3</SUB> with the CdS particles effectively accelerated charge separation and transfer in photocatalytic reactions due to the low density, hollow interior, and shell permeability of the onion-type composite. The optimized Co<SUB>4</SUB>S<SUB>3</SUB>/CdS photocatalyst led to an enhanced rate of H<SUB>2</SUB> production of 12,360μmolh<SUP>−1</SUP> g<SUP>−1</SUP> under simulated solar light irradiation; this value is 26-fold greater than that of the pristine CdS nanoparticles. The Co<SUB>4</SUB>S<SUB>3</SUB>/CdS composite exhibited remarkably stable photocatalytic performance for up to 65h and could be reused in five successive cycles. Furthermore, to the best of our knowledge, this is the highest H<SUB>2</SUB> production rate achieved with cobalt sulfide-based CdS nanoparticle photocatalysts in the photocatalysis of water under simulated solar light irradiation. Owing to its low cost and high efficiency, this photocatalytic system should hold great potential for the development of highly efficient photocatalytic materials for use in various fields.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Noble metal-free MOF-derived onion slice-type hollow structured Co<SUB>4</SUB>S<SUB>3</SUB> was developed. </LI> <LI> The Co<SUB>4</SUB>S<SUB>3</SUB> with the CdS particles effectively accelerated charge separation. </LI> <LI> The low density, hollow interior, shell permeability of Co<SUB>4</SUB>S<SUB>3</SUB> improves the transfer property. </LI> <LI> The optimized Co<SUB>4</SUB>S<SUB>3</SUB>/CdS shows high rate of H<SUB>2</SUB> production of 12,360μmolh<SUP>−1</SUP> g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Noble metal-free MOF-derived onion slice-type hollow cobalt sulfide nanostructures: Enhanced activity of CdS for improving photocatalytic hydrogen production by D.P. Kumar et al.</P> <P>[DISPLAY OMISSION]</P>

Multidirectional-charge-transfer urchin-type Mo-doped W₁₈O₄₉ nanostructures on CdS nanorods for enhanced photocatalytic hydrogen evolution

Bhavani, P.,Praveen Kumar, D.,Jeong, Seonghyun,Kim, Eun Hwa,Park, Hanbit,Hong, Sangyeob,Gopannagari, Madhusudana,Amaranatha Reddy, D.,Song, Jae Kyu,Kim, Tae Kyu The Royal Society of Chemistry 2018 Catalysis Science & Technology Vol.8 No.7

<P>Transition metal oxides (TMOs) have attracted attention because they provide eco-friendly ways of collecting solar energy and are more stable than sulfides or phosphides for photoirradiation over long periods without photocorrosion. Among TMOs, tungsten oxides have attracted considerable attention owing to their excellent electron transport properties and good resilience to photocorrosion in aqueous media. However, pristine WO3 exhibits low photocatalytic activity because of the rapid recombination of its photogenerated charge-carriers and its narrow photo-absorption range. Consequently, the monoclinic oxygen-deficient (WO3−δ) material W18O49 (≅WO2.73) has attracted greater interest than typical tungsten oxides due to its high chemical stability and large number of oxygen vacancies (OVs). In particular, the water splitting efficiency of W18O49 is enhanced by doping with Mo, which modifies the intrinsic chemical properties of W18O49 without disturbing the crystal structure while producing more active sites. Furthermore, by tuning the morphology of Mo-W18O49 (MWO), the photocatalytic activity of MWO-embedded CdS was greatly enhanced by the very large surface area and supplementary active sites. To that end, we developed an urchin-type MWO cocatalyst integrated into CdS nanorods (NRs) by simple methods. The catalyst exhibits an enhanced production rate of H2 (40.225 mmol h<SUP>−1</SUP> g<SUP>−1</SUP>) under simulated solar light irradiation, which is 20 times higher than that of pristine CdS NRs. The urchin-type morphology significantly shortens charge-carrier transport distances. The oxygen deficiency and Mo dopant in the W18O49 system also improve the number of active sites, which promotes the efficient utilization of light, excellent electron-transport properties, and good resilience to photocorrosion. These properties are especially beneficial for the effective excitation and separation of charge-carriers that are directed to the reduction of protons to H2. Moreover, to the best of our knowledge, this material exhibits the best performance among reported tungsten-based oxides as a cocatalyst on CdS composites.</P>