Solar-driven Wastewater Treatment Research Articles

Solar-driven photodegradation of ciprofloxacin and E. coli growth inhibition using a Tm3+ upconverting nanoparticle-based polymer composite

Solar-driven photocatalysis is of great interest in terms of a sustainable use of energy and its application in wastewater treatment. The UV light-driven photogeneration of H2O2 by solar irradiation is an advanced strategy for the treatment of bacteria and recalcitrant pollutants in wastewater, but suffers from low efficiencies. In this work, a solar-driven multifunctional nanocomposite consisting of Tm3+ upconverting nanoparticles, poly(vinyl alcohol), poly(acrylic acid) and hydroxylated sulfonated poly(ether ether ketone) was prepared. The components were crosslinked via a heating treatment at 170 °C, resulting in a non-leaching porous material. This nanocomposite exhibited excellent adsorption ability (89 % in 150 min) toward a 100 mg/L ciprofloxacin aqueous solution and proved to photodegrade it (50 %) upon 4 h artificial solar irradiation, exploiting photon upconversion processes. Moreover, an 80 % bactericidal effect against E. coli was registered upon sunlight irradiation. Altogether, these results suggest the feasibility of a solar-driven wastewater treatment based on upconverting nanoparticles.

Combined Structural and Plasmonic Enhancement of Nanometer-Thin Film Photocatalysis for Solar-Driven Wastewater Treatment.

Titanium dioxide (TiO2) thin films are commonly used as photocatalytic materials. Here, we enhance the photocatalytic activity of devices based on titanium dioxide (TiO2) by combining nanostructured glass substrates with metallic plasmonic nanostructures. We achieve a three-fold increase of the catalyst's surface area through nanoscale, three-dimensional patterning of periodic, conical grids, which creates a broadband optical absorber. The addition of aluminum and gold activates the structures plasmonically and increases the optical absorption in the TiO2 films to above 70% in the visible and NIR spectral range. We demonstrate the resulting enhancement of the photocatalytic activity with organic dye degradation tests under different light sources. Furthermore, the pharmaceutical drug Carbamazepine, a common water pollutant, is reduced in the aqueous solution by up to 48% in 360 min. Our approach is scalable and potentially enables future solar-driven wastewater treatment.

Plant-inspired multi-environmentally adaptive, flexible, and washable solar steam generation fabric

Interfacial solar water evaporation has been widely fabricated for water treatment owing to its great promise in harvesting fresh water with clean energy in need for carbon neural target. However, developing an evaporator with recyclability under severe contamination and adaptability for various complex aqueous environments, remains challenging. Herein, inspired by mangrove forest growing in salty shoals, an adaptive tree-like evaporator (ATE) was fabricated by rolling cotton threads and punched (pin-holed) carbon nanotube (CNT) film into modified photothermal bundles and further weaving them into root-leaf like structure, enabling uncoated cotton bundles as dense roots for extracting and transporting water and coated part as leaves with open holes for evaporation. Such a facile ATE showed stable water evaporation rate, and an excellent salt-self-cleaning performance. Importantly, the ATE was also available to extract and evaporate wastewater from some severe environments, such as mud, sand, emulsion and dye solution. The ATEs were scalable, and particularly proved to be flexible and robust for washing and reusing, with evaporation performance almost unchanged after 100 cycles. This work has demonstrated a prototype for an efficient, adaptive and scalable fabric evaporator for solar-driven wastewater treatment, opening the possibility to solve provisional freshwater supply in poverty-stricken or polluted areas.

Solar-driven wastewater treatment coupled with hydrogen and electricity production via a bismuth-doped TiO2 nanorod array

An ingenious and unassisted solar-driven wastewater resourcezation system (SDWRS) was designed by connecting a silicon cell (SC) to the back of a bismuth-doped TiO2 nanorod array (BTNR) for efficient water treatment accompanying hydrogen and electricity generation. Doping of Bi effectively improved the charge-transfer property and donor density of the BTNR. In addition, the introduction of SC provided an inner bias much higher than conventional photocatalytic fuel cells (PFCs) to drive efficient electron transfer from the photoanode to cathode by absorbing the transmitted longer wavelength photons. Therefore, compared with pure TNR, the photocurrent density of BTNR at 0.8 V vs Ag/AgCl is greatly increased to ∼2.81 mA cm−2. Due to the enhanced light utilization and charge transfer, which derived from the synergistic effect between the BTNR and SC, the assembled SDWRS displayed the outstanding tetracycline (TC) degradation together with hydrogen and electricity production. A TC removal ratio of nearly 100% after 2.5 h of operation, an average hydrogen generation rate of ∼29.08 μmol h−1 cm−2, and an electricity output with a maximum power output of ∼632.8 μW cm−2 were achieved. The results also manifested that SDWRS had great application potential for degrading various refractory pollutants from wastewater for clean energy production.

Antibacterial Evaporator Based on Wood-Reduced Graphene Oxide/Titanium Oxide Nanocomposite for Long-Term and Highly Efficient Solar-Driven Wastewater Treatment

Antibacterial Evaporator Based on Wood-Reduced Graphene Oxide/Titanium Oxide Nanocomposite for Long-Term and Highly Efficient Solar-Driven Wastewater Treatment

Construction of a Three-Dimensional Interpenetrating Network Sponge for High-Efficiency and Cavity-Enhanced Solar-Driven Wastewater Treatment.

It is well known that the photothermal conversion performance of solar-driven interfacial water evaporation systems is known to have a stronger photothermal conversion performance than suspended water evaporation systems due to their relatively strong ability to suppress overall heat loss. Natural polymer chitosan and gelatin can form a three-dimensional interpenetrating network (IPN) sponge to provide an interface for water evaporation due to strong hydrogen bonding and electrostatic attraction interaction. However, the lack of effective light absorption, the intrinsic short lifetime, and the poor photothermal conversion greatly compromise their steam generation performance. Here, we fabricated a chitosan/gelatin-based IPN sponge incorporated with melanin-coated titania hollow nanospheres (CG@MPT-h) as a solar thermal converter, which is designed to exhibit a unique cavity structure and vertical channels. The cavity structure of melanin-coated titania acts as a solar thermal transducer, while the chitosan/gelatin-based IPN sponge acts as a single-pass water pump. A water hyacinth-inspired evaporation system shows outstanding steam generation performance, and the highest steam generation rate was 3.17 kg m-2 h-1 under a 2.5 sun illumination because of the cavity enhancement effect, far above TiO2 particles and reported photo-thermal conversion materials. More importantly, the embedding of MPT-h nanoparticles in the IPN sponge effectively inhibits the growth of bacteria in the vertical channels, resulting in an antibacterial solar-driven water evaporator. This advanced sponge provides a cost-effective and practical sustainable energy technique for solar-driven wastewater treatment.

Recent Advances on Plasmon-enhanced Titania Nanocatalysts for Photocatalytic Degradation of Organic Dyes

In the past several years, solar-driven photocatalytic degradation of organic dyes has been considered as one of the most promising and effective ways to address water pollution issues. Nevertheless, the implementation of such technology for large scale industrial wastewater application is still hampered by the limitation in currently used photocatalysts. Recently, plasmon-enhanced titania-based nanocatalyst has emerged as one of the promising photocatalytic materials for solar-driven wastewater treatment due to its excellent activity and ability to absorb a large portion of solar radiation. Therefore, this review highlights recent progress on applying such material for the photodegradation of organic dyes. In this review, the focus is placed on several mechanisms on how the surface plasmon resonance (SPR) phenomenon could enhance the photocatalytic activity of semiconductors, such as TiO2. Furthermore, the performance of several types of plasmon-enhanced titania nanocatalyst with different kinds of metal plasmonic nanoparticles, i.e., Au-TiO2, Ag-TiO2, and Pd-TiO2, is also compared and comprehensively discussed. Finally, a particular emphasis is also given to highlight the nanocatalysts' kinetics in facilitating the photocatalytic degradation of different types of organic dyes.

Topology-Controlled Hydration of Polymer Network in Hydrogels for Solar-Driven Wastewater Treatment.

Solar-driven interfacial evaporation provides a promising method for sustainable freshwater production. However, high energy consumption of vapor generation fundamentally restricts practicality of solar-driven wastewater treatment. Here a facile strategy is reported to control the hydration of polymer network in hydrogels, where densely cross-linked polymers serving as a framework are functionalized by a highly hydratable polymeric network. The hydration of polymer chains generates a large amount of weakly bounded water molecules, facilitating the water evaporation. As a result, the hydrogel-based solar evaporator can extract water from a variety of contaminants such as salts, detergents, and heavy metal components using solar energy with long-term durability and stability. This work demonstrates an effective way to tune the interaction between water and materials at a molecular level, as well as an energy-efficient water treatment technology toward wastewater containing complex contaminants.

Ag nanoparticles deposited on oxygen-vacancy-containing BiVO4 for enhanced near-infrared photocatalytic activity

This study investigates the photodegradation of the organic dye rhodamine B by Ag-nanoparticle-containing BiVO4 catalysts under different irradiation conditions. The catalysts consist of Ag nanoparticles deposited on oxygen-vacancy-containing BiVO4. The morphology of the BiVO4 is olive shaped, and it has a uniform size distribution. The BiVO4 possesses a high oxygen vacancy density, and the resulting Ag nanoparticle-BiVO4 catalyst exhibits higher photocatalytic activity than BiVO4. The RhB degradation by the Ag nanoparticle-BiVO4 catalyst is 99% after 100 min of simulated solar irradiation. BiVO4 containing oxygen vacancies as a rationally designed support extends the catalyst response into the near-infrared region, and facilitates the trapping and transfer of plasmonic hot electrons. The enhanced photocatalytic efficiency is attributed to charge transfer from the BiVO4 to Ag nanoparticles, and surface plasmon resonance of the Ag nanoparticles. These insights into electron-hole separation and charge transfer may arouse interest in solar-driven wastewater treatment and water splitting.

A low-cost photoelectrochemical tandem cell for highly-stable and efficient solar water splitting

The stability and cost of solar-driven water splitting system are still the main bottlenecks for its large-scale implementation. Here, an ingeniously designed low-cost photoelectrochemical tandem cell possessing three performance-superior components, i.e., a front novel photoanode of WO3 nanoplates epitaxially coated with [001]-oriented TiO2 nanoprickles, and a rear Si photovoltaic cell, and a counter-cathode of interlayer-expanded MoS2 nanostructures, is reported for highly-stable and efficient solar water splitting. The tandem cell shows a close-to-unity Coulomb efficiency for water splitting, and a high and sustained-stable solar-to-hydrogen efficiency in a 35 days’ test. The result also reveals that it is versatile in solar-driven wastewater treatment. Most importantly, the composite photoanode that, for the first time, is proposed using epitaxial-growth based on double-match, i.e. lattice match and band match, shows dramatical improvement in stability and photoelectrochemical performance, in which the photocurrent of the WO3/ TiO2 photoanode is improved by 80% without any obvious decay after 100h of continuous testing compared with a 92% decay in photocurrent for the WO3 photoanode. The epitaxial TiO2 layer facilitates interfacial charge transportations and provides a complete sealing of WO3 surfaces at an atomic level. Such efficient interfacial design and system-level integration of high-performance nanomaterials shed a unique light on the potential large-scale implementation of solar water splitting for renewable hydrogen fuel production.

Synthesis and the enhanced visible-light-driven photocatalytic activity of BiVO4 nanocrystals coupled with Ag nanoparticles

BiVO4 nanocrystals coupled with Ag nanoparticles (Ag–BiVO4 heterogeneous nanostructures) have been prepared by a new strategy via combining a hydrothermal route with a polyol process, in which BiVO4 nanocrystals were first synthesized by a hydrothermal route, and then, Ag nanoparticles were grown on the surfaces of the presynthesized BiVO4 nanocrystals through a polyol process. The photocatalytic evaluations demonstrate that BiVO4 nanocrystals coupled with Ag nanoparticles exhibit the enhanced visible-light-driven photocatalytic activity for the degradation of methylene blue (MB) and rhodamine B (RhB). The energy alignment and diffuse reflectance property of Ag–BiVO4 heterogeneous nanostructures demonstrate that Ag nanoparticles attached on the surfaces of BiVO4 nanocrystals play double roles for the enhanced visible-light-driven photocatalytic activity. First, the Ag nanoparticles grown on the surfaces of BiVO4 nanocrystals may act as electron sinks to retard the recombination of the photogenerated electrons and holes in BiVO4 so as to improve the charge separation on its surfaces. Second, the Ag nanoparticles increase the visible light absorption of the Ag–BiVO4 photocatalyst due to surface plasmon resonance (SPR) of Ag nanoparticles. These double roles of Ag nanoparticles make Ag–BiVO4 heterogeneous nanostructures to exhibit the enhanced photocatalytic activity to decompose MB and RhB under visible light irradiation, compared to the pure BiVO4 nanocrystals. The enhanced photocatalytic activity is attributed to the charge transfer from BiVO4 to the attached Ag nanoparticles as well as SPR absorption of Ag nanoparticles. The present work not only provides an efficient route to enhance visible-light-driven photocatalytic activity of BiVO4, but also offers a new strategy for fabricating metal–semiconductor heterogeneous nanostructure photocatalysts, which are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.

P–n junction CuO/BiVO4 heterogeneous nanostructures: synthesis and highly efficient visible-light photocatalytic performance

A new strategy via coupling a polyol route with an oxidation process has been developed to successfully synthesize p-n junction CuO/BiVO4 heterogeneous nanostructures. The experimental results reveal that the as-prepared p-n junction CuO/BiVO4 heterogeneous nanostructures exhibit much higher visible-light-driven photocatalytic activity for the degradation of model dye rhodamine B (RhB) than the pure BiVO4 nanocrystals. The photocatalytic degradation rate (C/C0) of the RhB for p-n junction CuO/BiVO4 heterogeneous nanostructures is about two times higher than that of pure BiVO4 nanocrystals. The enhanced photocatalytic efficiency is attributed to a large number of p-n junctions in CuO/BiVO4 heterogeneous nanostructures, which effectively reduces the recombination of electrons and holes by charge transfer from n-type BiVO4 to the attached p-type CuO nanoparticles. This work not only provides an efficient route to enhance the visible-light-driven photocatalytic activity of BiVO4, but also offers a new strategy for fabricating p-n junction heterogeneous nanostructure photocatalysts, which are expected to show considerable potential application in solar-driven wastewater treatment and water splitting.

Preparation of p–n junction Cu2O/BiVO4 heterogeneous nanostructures with enhanced visible-light photocatalytic activity

p–n junction Cu2O/BiVO4 heterogeneous nanostructures for enhancement of visible-light photocatalytic properties of BiVO4 nanocrystals have been successfully prepared through coupling a hydrothermal process with polyol strategy. The assembly of p-type Cu2O nanoparticles produces a large number of nano p–n junction heterostructures on the surface of the BiVO4 nanocrystals, where Cu2O and BiVO4 form p- and n-type semiconductors, respectively. The experimental results reveal that these p–n junction Cu2O/BiVO4 heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO4 nanocrystals for the degradation of model dyes methylene blue and colorless organic phenol under visible light irradiation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from n-type BiVO4 to the attached p-type Cu2O nanoparticles, which effectively reduces the recombination of electrons and holes, leading to the enhancement of the photocatalytic properties of the heterostructure nanostructures. These new p–n junction heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment.

Preparation of Au-BiVO4 Heterogeneous Nanostructures as Highly Efficient Visible-Light Photocatalysts

Au-BiVO(4) heterogeneous nanostructures have been successfully prepared through in situ growth of gold nanoparticles on BiVO(4) microtubes and nanosheets via a cysteine-linking strategy. The experimental results reveal that these Au-BiVO(4) heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO(4) microtubes and nanosheets for both dye degradation and water oxidation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from BiVO(4) to the attached gold nanoparticles as well as their surface plasmon resonance (SPR) absorption. These new heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.