Gallo Junior, Adair; Farinha, Andreia S. F.; Emwas, Abdul-Hamid M.; Santana, Adriano; Nielsen, Robert J.; Goddard, William A.; Mishra, Himanshu(Chemical Science, Royal Society of Chemistry (RSC), 2019-07-23)[Article]
The air–water interface serves as a crucial site for numerous chemical and physical processes in environmental science and engineering, such as cloud chemistry, ocean-atmosphere exchange, and wastewater treatment. The development of “surface-selective” techniques for probing interfacial properties of water therefore lies at the forefront of research in chemical science. Recently, researchers have adapted electrospray ionization mass spectrometry (ESIMS) to generate microdroplets of water to investigate interfacial phenomena at thermodynamic equilibrium. In contrast, using a broad set of experimental and theoretical techniques, we found that electrosprays of water could facilitate partially hydrated (gas-phase) ions (e.g., H3O+·(H2O)2) to drive/catalyze chemical reactions that are otherwise not possible to accomplish by purely interfacial effects (e.g., enhanced water–hydrophobe surface area) (Chem. Sci., 2019, 10, 2566). Thus, techniques exploiting electrosprays of water cannot be relied upon as generalized surface-selective platforms. Here, we respond to the comments raised by Colussi & Enami (Chem. Sci., 2019, 10, DOI: 10.1039/c9sc00991d) on our paper.
Wang, Shaofei; Mahalingam, Dinesh; Sutisna, Burhannudin; Nunes, Suzana Pereira(Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2019)[Article]
Two-dimensional (2D) lamellar membranes are highly advantageous in molecular separations. However, the permeance-rejection trade-off is always a major challenge, since the permeant transport mostly occurs in single-spacing channels with undesired microenvironments. Inspired by the structure of aquaporins, we design alternating dual-spacing channel graphene oxide (GO) membranes, with locally tailored chemical microenvironments, that give high permeance, high rejection and high stability in organic solvent nanofiltration. This unique structure is easily constructed by in situ intercalating and cross-linking scattered sub-5 nm silica nanoparticles in the GO interlayers. The hydrophilic nanoparticles locally widen the interlayer channels to enhance the solvent permeance. In the alternating nanoparticle-free areas, the GO layers simultaneously bend and the π–π interactions retain the narrow and hydrophobic channels, promoting high solute rejection. With a 10-fold increase in water permeance and unaffected rejection, the dual-spacing channel membranes exhibit one of the best performances for organic solvent nanofiltration. The methanol permeance reaches 290 L m−2 h−1 bar−1, with more than 90% rejection of dyes larger than 1.5 nm. This new approach of designing hierarchical channels in 2D materials can be used for a wide spectrum of applications.
Gallo Junior, Adair; Farinha, Andreia S. F.; Dinis Veloso Guerreiro, Miguel; Emwas, Abdul-Hamid M.; Santana, Adriano; Nielsen, Robert J.; Goddard, William A.; Mishra, Himanshu(Chemical Science, Royal Society of Chemistry (RSC), 2018-12-21)[Article]
The recent application of electrosprays to characterize the air–water interface, along with the reports on dramatically accelerated chemical reactions in aqueous electrosprays, have sparked a broad interest. Herein, we report on complementary laboratory and in silico experiments tracking the oligomerization of isoprene, an important biogenic gas, in electrosprays and isoprene–water emulsions to differentiate the contributions of interfacial effects from those of high voltages leading to charge-separation and concentration of reactants in the electrosprays. To this end, we employed electrospray ionization mass spectrometry, proton nuclear magnetic resonance, ab initio calculations and molecular dynamics simulations. We found that the oligomerization of isoprene in aqueous electrosprays involved minimally hydrated and highly reactive hydronium ions. Those conditions, however, are non-existent at pristine air–water interfaces and oil–water emulsions under normal temperature and pressure. Thus, electrosprays should be complemented with surface-specific platforms and theoretical methods to reliably investigate chemistries at the pristine air–water interface.
Shi, Le; Zhuo, Sifei; Abulikemu, Mutalifu; Mettela, Gangaiah; Palaniselvam, Thangavelu; Rasul, Shahid; Tang, Bo; Yan, Buyi; Saleh, Navid B.; Wang, Peng(RSC Advances, Royal Society of Chemistry (RSC), 2018-08-16)[Article]
The effects of annealing treatment between 400 °C and 540 °C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO4) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO4 thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO4 thin film prepared at a higher annealing temperature (500–540 °C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm−2 to 1.27 mA cm−2 and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm−2 for the samples prepared from 400 °C to 540 °C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO4 samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO4 samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (Cdl). Cdl was 0.0074 mF cm−2 at 400 °C and it decreased to 0.0006 mF cm−2 at 540 °C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk (ηbulk) and on the surface (ηsurface) of the BiVO4 thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.
Bian, Bin; AlQahtani, Manal Faisal; Katuri, Krishna; Liu, Defei; Bajracharya, Suman; Lai, Zhiping; Rabaey, Korneel; Saikaly, Pascal(Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2018-08-15)[Article]
Microbial electrosynthesis (MES) allows recycling of CO into value added products by coupling renewable energy to the microbial ability for complex product formation. To improve biofilm formation on the cathode and the rates of product generation, the design of cathodes possessing a high specific surface area and enhanced electrode-microbe electron transfer is needed. This study aimed to demonstrate a novel cathode design that is made of porous nickel hollow fibers (Ni-PHFs), for facilitating direct delivery of CO to Sporomusa ovata in MES through the pores in the hollow fibers. Modification of the surface of Ni-PHFs with carbon nanotubes (CNTs) resulted in an 11-fold increase in the CO adsorption capability at atmospheric pressure, as well as 76.3% reduction of cathode electron transfer resistance. This cathode surface modification partially explained the higher acetate production rate of 247 ± 17 mM d m from direct CO delivery through the pores of the Ni-PHF/CNT cathode, compared to 145 ± 4 mM d m for the Ni-PHF cathode. Higher electron recovery in the form of acetate (∼83%) was also observed for the Ni-PHF/CNT cathode. As for the tests where CO was sparged into the medium, acetate production was 36% lower than tests with direct CO delivery to S. ovata through the pores of the Ni-PHF/CNT cathode. These results demonstrate that using the PHF electrode design and modifying the cathode morphology to enhance the microbe-electrode interactions and CO availability for bacterial growth are effective approaches to increase the rates of CO reduction in MES.
Chang, Jian; Shi, Yusuf; Wu, Mengchun; Li, Renyuan; Shi, Le; Jin, Yong; Qing, Weihua; Tang, Chuyang; Wang, Peng(Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2018-04-16)[Article]
Rapid cleanup of heavy oil spill is always considered as a great challenge because the conventional porous oil sorbents cannot efficiently remove them due to the high viscosity of the oil (>1000 mPa·s). In this work, we take advantage of the photothermal effect to heating the heavy oil by using sunlight as energy source to significantly reduce the viscosity of the heavy oil and thus to achieve a fast heavy oil cleanup. A carbon nanotube (CNT) modified polyurethane sponge was fabricated as photothermal sorbent that exhibited superhydrophobicity, superoleophilicity, as well as outstanding absorption capacity of heavy oil. Thanks to the excellent photothermal effect of CNTs, the modified sponge achieved nearly full sunlight absorption (99%). The resulting solar heating effectively reduced the viscosity of the heavy oil, which enabled the modified sponge to quickly absorb heavy oil of 20 times its own weight under sun illumination. This solar-assisted heavy oil sorbent design is promising for future remediation of viscous oil-spills.
Wang, Peng(Environmental Science: Nano, Royal Society of Chemistry (RSC), 2018-04-05)[Article]
Solar driven water evaporation and distillation is an ancient technology, but has been rejuvenated by nano-enabled photothermal materials in the past 4 years. The nano-enabled state-of-the-art photothermal materials are able to harvest a full solar spectrum and convert it to heat with extremely high efficiency. Moreover, photothermal structures with heat loss management have evolved in parallel. These together have led to the steadily and significantly improved energy efficiency of solar evaporation and distillation in the past 4 years. Some unprecedented clean water production rates have been reported in small-scale and fully solar-driven devices. This frontier presents a timely and systematic review of the impressive developments in photothermal nanomaterial discovery, selection, optimization, and photothermal structural designs along with their applications especially in clean water production. The current challenges and future perspectives are provided. This article helps inspire more research efforts from environmental nano communities to push forward practical solar-driven clean water production.
Jin, Yong; Chang, Jian; Shi, Yusuf; Shi, Le; Hong, Seunghyun; Wang, Peng(Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2018-03-29)[Article]
Solar-driven water evaporation is emerging as a promising solar-energy utilization process. In the present work, highly stable, flexible and washable nonwoven photothermal cloth is prepared by electrospinning for efficient and durable solar steam evaporation. The cloth is composed of polymeric nanofibers as matrix and inorganic carbon black nanoparticles encapsulated inside the matrix as light absorbing component. The photothermal cloth with an optimized carbon loading shows a desirable underwater black property, absorbing 94% of the solar spectrum and giving rise to a state-of-the-art solar energy utilization efficiency of 83% during pure water evaporation process. Owing to its compositions and special structural design, the cloth possesses anti-photothermal-component-loss property and is highly flexible and mechanically strong, chemically stable in various harsh environment such as strong acid, alkaline, organic solvent and salty water. It can be hand-washed for more than 100 times without degrading its performance and thus offers a potential mechanism for foulant cleaning during practical solar steam generation and distillation processes. The results of this work stimulate more research in durable photothermal materials aiming at real world applications.
Myung, Jaewook; Yang, Wulin; Saikaly, Pascal; Logan, Bruce E(Environmental Science: Water Research & Technology, Royal Society of Chemistry (RSC), 2018-02-05)[Article]
Long-term operation of wastewater-fed, microbial fuel cells (MFCs) with cathodes made of activated carbon and stainless steel (SS) current collectors can result in decreased performance due to cathode fouling. Copper has good antimicrobial properties, and it is more electrically conductive than SS. To demonstrate that a copper current collector could produce a more fouling resistant cathode, MFCs with air cathodes using either SS or copper current collectors were operated using domestic wastewater for 27 weeks. The reduction in biofouling over time was shown by less biofilm formation on the copper cathode surface compared to SS cathodes, due to the antimicrobial properties of copper. Maximum power densities from 17–27 weeks were 440 ± 38 mW/m2 using copper and 370 ± 21 mW/m2 using SS cathodes. The main difference in the microbial community was a nitrifying community on the SS cathodes, which was not present on the copper cathodes.
Chang, Jian; Zhang, Lianbin; Wang, Peng(Environmental Science: Nano, Royal Society of Chemistry (RSC), 2018-01-30)[Article]
Due to the inherent complexity of environmental problems, especially water and air pollution, the utility of single-function environmental nanomaterials used in conventional and unconventional environmental treatment technologies are gradually reaching their limits. Intelligent nanomaterials with environmentally-responsive functionalities have shown potential to improve the performance of existing and new environmental technologies. By rational design of their structures and functionalities, intelligent nanomaterials can perform different tasks in response to varying application scenarios for the purpose of achieving the best performance. This review offers a critical analysis of the design concepts and latest progresses on the intelligent environmental nanomaterials in filtration membranes with responsive gates, materials with switchable wettability for selective and on-demand oil/water separation, environmental materials with self-healing capability, and emerging nanofibrous air filters for PM2.5 removal. We hope that this review will inspire further research efforts to develop intelligent environmental nanomaterials for the enhancement of the overall quality of environmental or human health.
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