Co-adsorption enhancement of formaldehyde/carbon dioxide over modified hexagonal boron nitride for whole-surface capture purification.

Simultaneous capture of formaldehyde (HCHO) and carbon dioxide (CO2) in indoor air is promising of achieving indoor-air purification. Of all potential adsorbents, hexagonal boron nitride (h-BN) is one of the most suitable species owing to facile formation of attraction points. Therefore, in this study, performances of HCHO and CO2 being adsorbed over pure/modified h-BN are systematically investigated via density functional theory (DFT) calculations. Minutely speaking, direct interaction between HCHO and CO2, single-point adsorption enhancement of HCHO over modified h-BN, co-adsorption reinforcement of HCHO/CO2 as well as relevant thermodynamic characteristics are major research contents. According to calculation results, there is relatively strong attraction between HCHO and CO2 owing to hydrogen bonds, which is in favor of co-adsorption of HCHO/CO2. As to single-adsorption of HCHO, C-doped h-BN shows better adsorption features than P-doped h-BN and C/P-doped h-BN is slightly weakened in adsorption ability due to surficial deformation caused by P atoms. For co-adsorption of HCHO/CO2, CO2 is the protagonist via formation of quasi-carbonate with the help of delocalized π-orbital electrons. Regarding effects of temperatures on adsorption strengths, they depend on interelectronic interactions among dopant atoms and finally derives from dispersion of π bonds across adsorbents. Overall, this study provides detailed mechanisms for co-capture of HCHO/CO2 to accomplish indoor-air purification.

Research progress of vanadium pentoxide photocatalytic materials.

Photocatalytic reactions convert solar energy into chemical energy through a clean and green reaction process. Photocatalytic technology based on semiconductor materials provides us with a new idea in energy utilization and environmental governance. It was found that vanadium pentoxide (V2O5) has a narrow band gap, wide response range in the visible region, high oxygen density in the V2O5 lattice, high oxidation state of V5+, small energy requirement, and superior catalytic activity in partial oxidation. Therefore, the utilization rate of sunlight and photocatalytic oxidation can be greatly improved using V2O5 materials. However, the narrow band gap of V2O5 also makes it easier for the photogenerated electrons and holes to recombine in the excited state, and the stored energy is instantly consumed by carrier recombination. Therefore, how to promote the carrier separation of V2O5 and improve the photocatalytic efficiency are the key problems to be solved. Herein, several methods to improve the photocatalytic performance of V2O5 are reviewed, including metallic ion doping, non-metallic ion doping, semiconductor recombination, and noble metal deposition. Finally, it is suggested that future research directions should focus on a variety of modification methods simultaneously to promote photocatalytic efficiency and lower the cost, which will enable V2O5 to have a broad development prospect in the field of photocatalysis.

Optimized nano-metal particles filled into carbon nanohorns to achieve high N-doping amount and high porosity for enhanced oxygen evolution reaction.

Nano-metal-filled N-doped carbon materials have been actively verified as promising alternatives for precious-metal catalysts in the oxygen evolution reaction (OER). Herein, Ni/Fe/Cu-filled N-doped carbon nanohorns (CNHs) are synthesized via a positive pressure assisted arc discharge method using a Ni/Fe/Cu rod charged in an anode hole in a N2 and Ar mixture. We first found that the amount of N atom doping can be controlled by the types of nano-metal particles encapsulated by CNHs. The content of N atoms on CNHs uniquely depended on the initial Ni wires inserted into the anode graphite; increasing the number of Ni wires induced the enrichment of N atoms until 3.56 at%, whereas the content of N atoms for Cu- and Fe-filled CNHs is against the results; loading Cu and Fe nanoparticles decreases the N-doping amount. And the morphologies and N-configurations can be changed by the types of metal nanoparticles. Furthermore, the OER performance of Ni-filled CNHs is much superior to that of Cu- and Fe-filled CNHs, which can be significantly enhanced by the tip opening structure, and the increase in Ni loading amount and the N atom content.

Controllable Synthesis of Mo3C2 Encapsulated by N-Doped Carbon Microspheres to Achieve Highly Efficient Microwave Absorption at Full Wavebands: From Lemon-like to Fig-like Morphologies.

Mo3C2@N-doped carbon microspheres (Mo3C2@NC) have been discovered to be a family of superior microwave absorbing materials. Herein, Mo3C2@NC was synthesized through a simple high-temperature carbonization process by evaporating a graphite anode and Mo wire in Ar and N2 atmospheres with an N-doping content of 6.4 at. %. Attributing to the self-assembly mechanism, the number of Mo wires inserted into the graphite anode determined the morphologies of Mo3C2@NC, which were the unique lemon-like (1- and 2-Mo3C2@NC) and fig-like (3-, 4-, and 5-Mo3C2@NC) microstructures. 1- and 2-Mo3C2@NC exhibited powerful reflection losses (RLs) of -45.60, -45.59, and -47.11 dB at the S, C and X bands, respectively, which corresponded to thinner thicknesses. 3-, 4-, and 5-Mo3C2@NC showed outstanding absorption performance at the C, X, and Ku bands, respectively, with each value of a minimum RL less than -43.00 dB. In particular, the strongest RL (-43.56 dB) for 5-Mo3C2@NC corresponded to an ultrathin thickness of 1.3 mm. In addition, the maximum effective absorption bandwidth was 6.3 GHz for 4-Mo3C2@NC. After analysis, all Mo3C2@NC samples showed well-matched impedance due to the enhanced dielectric loss caused by the unique carbon structure and moderate magnetic loss derived from the weak magnetic property of Mo3C2. More importantly, the unique lemon-like and fig-like microstructures created sufficient interfaces and differentiated multiple reflection paths, which greatly contributed to the strong microwave absorptions at full wavebands. In full consideration of the simple preparation method and tunable absorption properties, Mo3C2@NC composites can be regarded as excellent electromagnetic wave absorption materials.

Optimized Nanopores Opened on N-Doped Carbon Nanohorns Filled with Fe/Fe2O3 Nanoparticles as Advanced Electrocatalysts for the Oxygen Evolution Reaction.

N-doped carbon nanohorns filled with Fe nanoparticles (Fe-N-CNHs) were produced by one-step positive pressure-assisted arc discharge in the Ar and N2 mixture. After oxidation treatments in air, Fe was converted into Fe2O3, and nanopores were opened on CNHs from 1 to 5 nm controlled by oxidation temperature. Fe-N-CNHs oxidized in O2 at 550 °C (Fe2O3-N-CNH550ox) show 245 mV at 20 mA cm-1, which is much smaller than that of the ones oxidized at 500 °C (Fe2O3-N-CNH500ox), contributing to the larger pore size on CNHs (3-5 nm vs 2-3 nm) and a larger number of nanopores caused by the enhanced sidewall nanopores. However, the stability of Fe2O3-N-CNH550ox becomes much poorer than that of Fe2O3-N-CNH500ox after 2000 cycles. The unique relationship between the overpotential and long-term stability can be explained by the consideration of the size of Fe2O3 nanoparticles and nanopores on CNHs. Furthermore, the stability for Fe2O3-N-CNH550ox can be rapidly increased after heat treatment in Ar for 1 h caused by shrinking the size of tip nanopores. Herein, we first reveal that the performance of OER is related to the nanopore size of carbon carriers and the catalyst of nanometal particles. The optimization of pore-opening conditions in carbon carriers can be achieved a superior electrocatalytic OER performance, including a low overpotential at high current density and long-term stability.

Controllable synthesis of N-doped carbon nanohorns: tip from closed to half-closed, used as efficient electrocatalysts for oxygen evolution reaction.

The development of efficient, cost-effective and stable N-doped carbon material with catalytic activity as an excellent catalyst for the oxygen evolution reaction (OER) is critical for renewable energy systems. In this study, the unique tip-half-closed N-doped carbon nanohorns (THC-N-CNHs) were firstly produced by the positive pressure-assisted arc discharge method using N2 as the nitrogen source. Benefitting from the novel tip-half-closed structure and sufficient porosity, the specific surface area (SSA) of THC-N-CNHs is calculated to be 670 m2 g-1 without any further treatment, which is three times larger than that of traditional tip-closed CNHs. More importantly, the content of nitrogen can achieve ∼1.98 at% with noticeable pyridinic-N enrichment, increasing the number of active sites for the OER. Furthermore, the three-dimensional spherical feature and the unique pore structure for THC-N-CNHs lead to the fast transportation of electrons, and facile release of the evolved O2 bubbles during the OER process. Therefore, THC-N-CNHs exhibit excellent electrocatalytic activity toward the OER, with an overpotential of 328 mV at 10 mA cm-2, which is superior to that of most N-doped carbon material-based electrocatalysts. Meanwhile, the resulting catalyst also shows excellent durability after long-term cycling. Finally, we emphasize that THC-N-CNHs can be promising candidates as cheap, industrially scalable catalytic scaffolds for OER application.

Ni-Based Nanoparticle-Embedded N-Doped Carbon Nanohorns Derived from Double Core-Shell CNH@PDA@NiMOFs for Oxygen Electrocatalysis.

The development of highly efficient electrocatalysts for the oxygen evolution reaction (OER) plays a crucial role in many regenerative electrochemical energy-conversion systems. Herein, we report a novel double core-shell-structured CNH@PDA@NiMOF (CNH-D-NiMOF) composite based on the support of carbon nanohorns (CNHs) and the direction of polydopamine (PDA) on the synthesis of metal-organic frameworks (MOFs). It is found that this unique structure improves the electrocatalytic performance and stability of the composites. Furthermore, a controlled partial pyrolysis strategy was proposed to construct the Ni-based nanoparticle-embedded N-doped CNHs. The partial pyrolysis method preserves the framework structure of MOFs for effective substrate diffusion while producing highly active nanoparticles. This leads to the result that the Ni-based nanoparticle-embedded N-doped CNHs possess higher stability and significantly improved electrocatalytic properties. Among these derivatives, the sample prepared at a pyrolysis temperature of 400 °C (named as CNH-D-NiMOF-400) outperforms most of the reported unprecious-metal catalysts. At current densities of 20 and 100 mA·cm-2, the overpotentials of CNH-D-NiMOF-400 are 270 and 340 mV for the OER on a carbon fiber paper (CFP), respectively. The outstanding electrocatalytic properties above suggest that this composite is an excellent candidate for the substitution of noble metal-based catalysts for OER.

The Kinetics and Mechanisms for Photodegradation of Nitrated Polycyclic Aromatic Hydrocarbons on Lettuce Leaf Surfaces: An In Vivo Study.

Insights into the environmental fates of nitrated polycyclic aromatic hydrocarbons (NPAHs) in edible vegetables are of great significance for better evaluating human exposure to NPAHs through the dietary pathway. In this work, a fluorescence quenching method using graphene quantum dots as a fluorescent probe was first applied for the in vivo determination of 9-nitroanthracene (9-NAnt) and 1-nitropyrene (1-NPyr) adsorbed on the leaf surfaces of living lettuce (Lactuca sativa L.) seedlings. Moreover, the photolysis kinetics and mechanisms of the two adsorbed NPAHs were discussed. The photodegradation kinetics followed the pseudo-first-order equation, and the photodegradation half-life of 1-NPyr (7.4 ± 0.2 h) was greater than that of 9-NAnt (2.3 ± 0.1 h). Anthraquinone and pyrenediones were identified to be the main photolytic products of 9-NAnt and 1-NPyr, respectively. Intramolecular rearrangement was the most reasonable mechanism for the NPAH photolysis. The photolysis-driven degradation exhibited a key role in scavenging NPAHs from the vegetable leaf, indicating the reduction of NPAH transportation in the food chain.

Insight into effects of citric acid on adsorption of phthalic acid esters (PAEs) in mangrove sediments.

The adsorption of phthalate esters (PAEs) in mangrove sediment greatly influences their availability to aquatic organisms, however, the adsorption processes of PAEs in mangrove sediment, as well as the effects of root exudates, are poorly understood. In this study, dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP) was used as model PAEs to determine the effects and mechanism of citric acid on the adsorption kinetics and isotherms of PAEs in the mangrove sediments. The adsorption kinetics followed pseudo-second order model, describing the characteristics of heterogeneous chemisorption of PAEs in mangrove sediments. The adsorption isotherms of DMP and DEP followed Freundlich model, implying the characteristics of surface multilayer heterogeneous adsorption; while the Henry model better described the adsorption isotherms of DBP, suggesting that hydrophobic partition accounted for DBP adsorption in the mangrove sediments. Inter-chemical variability was observed in adsorption capacity (qe) with the sequence of DBP > DEP > DMP. Surface polarity index ((C-O + COOH + C˭O)%) of particulate organic matter (POM) regulated the adsorption capacity of DMP and DEP in mangrove sediments, while different POM content among mangrove sediments explained the difference in the sorption strength for DBP. The presence of citric acid enhanced the qe of the three PAEs by 6.4-12.6%. These findings are of great significance to reveal that the root exudates play a crucial role in the PAEs adsorption in mangrove sediments, and provide valuable information for availability of PAEs in mangrove ecosystem.

Novel method for in situ investigation into graphene quantum dots effects on the adsorption of nitrated polycyclic aromatic hydrocarbons by crop leaf surfaces.

Nitrated polycyclic aromatic hydrocarbons (NPAHs) are PAH derivatives with more toxic effects to ecosystem, and the partitioning of NPAHs in crop system constitutes the potential exposure to human health through the dietary pathway. In the present study, a novel method for in situ detection of 9-nitroanthracene (9-NAnt) and 3-nitrofluoranthene (3-NFla) adsorbed onto the leaf surfaces of living soybean and maize seedlings was established based on the fiber-optic fluorimetry combined with graphene quantum dots (GQDs) as a fluorescent probe. The detection limits for the in situ quantification of the two adsorbed NPAHs ranged from 0.8 to 1.6 ng/spot (spot represents determination unit, 0.28 cm2 per spot). Using the novel method, the effects of GQDs on the adsorption of individual 9-NAnt and 3-NFla by the living soybean and maize leaf surfaces were in situ investigated. The presence of GQDs altered the adsorption mechanism from the sole film diffusion to the combination of film diffusion and intra-particle diffusion, and shortened the time required to achieving adsorption equilibrium by 15.8-21.7%. Significant inter-species and inter-chemical variability existed in terms of the equilibrated adsorption capacity (qe) with the sequence of soybean > maize and 3-NFla > 9-NAnt. The occurrence of GQDs enlarged the qe values of 9-NAnt and 3-NFla by 22.8% versus 28.7% for soybean, and 16.2% versus 20.3% for maize, respectively, which was largely attributed to GQDs-induced expansion to the surface area for adsorbing NPHAs and the stronger electrostatic interaction between the -NO2 of NPAH molecules and the functional groups (e.g., -COOH, -OH) of GQDs outer surfaces. And, the varied enhancement degrees in the order of 3-NFla > 9-NAnt might be explained by the steric effects that resulted in the easier accessibility of -NO2 of 3-NFla to the outer surface of GQDs. Summarily, the GQDs increased the retention of NPAHs on crop leaf surfaces, potentially threatening the crop security.

Direct determination of surfactant effects on the uptake of gaseous parent and alkylated PAHs by crop leaf surfaces.

The partitioning of atmospheric polycyclic aromatic hydrocarbons (PAHs) into crop systems raises concerns about their potential harm to ecosystem and human health. To assess parent and alkylated PAHs accumulation accurately, the uptake of individual 7-isopropyl-1-methylphenanthrene (Retene), 3-methyl-phenanthrene (3-MP) and phenanthrene (Phe) by living maize, soybean and potato leaf surfaces, as well as the effects of cationic cetyltrimethylammonium bromide (CTMAB) and anionic sodium dodecyl benzene sulfonate (SDBS), were examined in situ using fiber-optic fluorimetry. For each of three PAH chemicals, the uptake achieved equilibrium between the air and living crop leaf surfaces within the 120-h monitoring period. There is inter-chemical and inter-species variability in terms of both the time required reaching equilibrium, the equilibrated adsorption concentration (EAC) and the overall air-surfaces mass transfer coefficient (kAS). The EAC of the three PAHs for each of the three crops' leaf surfaces increased with the number of alkyl substitutions on the aromatic ring. For any given PAHs, the EAC values followed the sequence of potato > soybean > maize, which was dominantly controlled by their leaf surface polarity index ((O+N)/C). The presence of CTMAB and SDBS increased the EAC of PAHs in the three crops' leaf surfaces by 6.5-17.1%, due to the plasticizing effect induced by the surface-sorbed surfactants, and the enhancement degree was closely associated with leaf-wax content and lg KOW values of PAHs. In addition, the two surfactants promoted the kAS values of the three chemicals by 7.7-23.3%. These results demonstrated that surfactants promoted the uptake of PAHs onto the crop leaf surfaces, potentially threatening the agricultural product safety.

In-situ examination of graphene and graphene oxide impact on the depuration of phenanthrene and fluoranthene adsorbed onto spinach (Spinacia oleracea L.) leaf surfaces.

To further assess the human being's exposure to polycyclic aromatic hydrocarbons (PAHs) through the dietary pathway, understanding the partitioning of these chemicals co-existed with nanomaterials in edible vegetable systems deserves specific consideration. In this study, the fiber-optic fluorimetry was applied to in situ examine the effects of graphene (GNS) and graphene oxide (GO) nanosheets on the quantification and depuration of three-ringed phenanthrene (Phe) and four-ringed fluoranthene (Fla) adsorbed individually onto the living spinach (Spinacia oleracea L.) surfaces. When the GNS and GO dosages separately increased to the maximum values: a respective red-shift of 4-5 nm and blue-shift of 2-3 nm occurred for the optimal detection emission wavelengths (λem) of the two PAHs, indicating that individual GNS and GO resulted in different changes to the epicuticular wax (ECW) polarity; GNS-inducing fluorescence quenching for the PAHs was about two times greater than GO, owing to the stronger π-π interactions between PAH molecules and GNS relative to GO; the volatilization coefficients (kC1) were reduced by 31.1% versus 26.7% for Phe, and 51.6% versus 34.4% for Fla, mainly via providing an additional adsorbent and promoting the accessibility of the leaf cuticle; respective photolysis coefficients (kP2) of Phe and Fla decreased by 42.9% and 50.0% with GNS, primarily owing to the enhancement of the ECW light-adsorption capacity, but increased by 33.3% and 40.0% with GO due to its photocatalytic activities; overall, total depuration coefficients (kT1, kT2) of the two PAHs decreased by 11.1-55.6%. These findings demonstrate that GNS and GO significantly alter the depuration behavior of PAHs in vegetable systems, potentially posing a threat to the safety of edible vegetables.