Secondary Calcination Research Articles

Iron mediated n → π* electron transitions and mid-gap states formation in CN under low-temperature secondary calcination enhances photodegradation of organic pollutants

Iron modified carbon nitride (CN) materials have attracted widespread attention from researchers in different application fields. In this paper, single atom iron anchored CN (FeCN) with mid-gap states and n → π* electron transition was synthesized through low temperature secondary calcination. The mid-gap states introduce surface states capable of trapping photogenerated electrons, enabling FeCN to absorb photons with energies lower than its intrinsic optical bandgap. 10%FeCN also exhibits distinct optical absorption above 490 nm derived from the n → π* electron transition, which expand the visible light response range of photocatalysts and enhance electron transport ability. Additionally, the Fe-Nx site enhances the separation and transmission efficiency of photoexcited charges. The prepared 10%FeCN exhibits extremely high photocatalysis and photo-Fenton activity. Mercaptobenzothiazole (MBT) degradation rate of 10%FeCN is 3.47 times higher than CN, achieving a mineralization rate of 86.7% in 100 min. Additionally, the oxytetracycline hydrochloride (OTC) degradation rate of 10%FeCN in photo-Fenton reaction is 11.9 times higher than CN. After five cycles, this catalyst still has good reactivity, indicating its good stability.

The induced formation and regulation of closed-pore structure for biomass hard carbon as anode in sodium-ion batteries

Biomass hard carbon is regarded as an advanced anode materials for sodium ion batteries (SIBs) since it possesses balanced performance including satisfactory specific capacity, suitable operating voltage window and low cost. Although numerous instances of utilizing biomass-derived hard carbon in SIBs have been observed, the unregulated pore structure of these hard carbon materials significantly constrains the electrochemical performance of SIBs, leading to diminished initial Columbic efficiency (ICE) and plateau capacity. Herein, taking a biomass hard carbon derived from waste camellia seed shells (CSSHCs) as a template, we display a correlation between synthesis conditions and pore structure of CSSHCs. CSSHCs are synthesized via a facile route including pre‑carbonization, purifying, mechanical ball-milling and high-temperature carbonization, and it is found that adjusting the secondary calcination temperature can induce the formation of closed pore structure, which is of great benefit to increase the ICE and the plateau-capacity. Besides, it is also proved that the obtained CSSHCs anodes obey a sodium storage mechanism that can be classified as “adsorption-intercalation-pore filling”, which endows SIBs with a competitive electrochemical performance. Specifically, the obtained biomass hard carbons at 1300 °C exhibits the best electrochemical performance among these anodes with the reversible capacity of as high as 270.0 mAh g−1 and a high ICE of 80.1 %, together with an excellent cycle stability (91.0 % capacity retention after 200 cycles at 0.1C, 1C = 300 mA g−1). Therefore, this study provides a significant exploration and raw material support for the further utilization of the waste biomass and sustainable development of the anode materials for the large-scale application of SIBs.

Simple preparation of ultra‐thin white g‐C3N4 nano‐sheets and their use as nanofillers to enhance the tribological properties of epoxy composite coating

AbstractGraphite phase carbon nitride (g‐C3N4) has shown great promise as a functional filler in the field of friction. But at present, research in the field of friction mainly focuses on bulk g‐C3N4 or obtaining g‐C3N4 nano‐sheets through inefficient exfoliation strategies, which greatly limits its industrial applications. In the study, a simple and effective secondary calcination method has been developed to successfully fabricate ultrathin white g‐C3N4 nano‐sheets. The mass ratio of the same volume of bulk g‐C3N4 and white g‐C3N4 nano‐sheets was as high as 50:1. Subsequently, the tribological performance of epoxy (EP) composite coatings containing different contents of bulk g‐C3N4 and g‐C3N4 nano‐sheets were researched. The EP composite coatings containing 1 wt.% g‐C3N4 nano‐sheets possess the lowest wear rate and friction coefficient in all samples, which is attributed to the two‐dimensional planar structure and high specific surface area of g‐C3N4 nano‐sheets make it easier to transfer to the dual surface to form the excellent transfer film under the action of friction force, so that the friction mainly occurs between a dual surface and a transfer film, which effectively improves the tribological performance of the coatings.Highlights Ultrathin white g‐C3N4 nano‐sheets were prepared by secondary calcination. EP‐1 wt.% g‐C3N4 nanosheets show the best tribological properties. g‐C3N4 nanosheet is easy to transfer to dual surfaces to form transfer films. This work provides guidance for the application of nanofillers in tribology.

Synchronous reinforcement azo dyes decolorization and anaerobic granular sludge stability by Fe, N co-modified biochar: enhancement based on extracellular electron transfer

Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

Construction of core-shell heterostructures Co3S4@NiCo2S4 as cathode and covalent organic framework derived carbon as anode for hybrid supercapacitors

Structured design helps to play out the coordination advantage and optimize the performance of electrochemical reactions. In this work, hierarchical hollow microspheres (Co3S4@NiCo2S4) with unique core-shell heterostructure were successfully prepared through simple template and solvothermal methods. Thanks to the hollow structure, cross-linked nanowire arrays, and in-situ coating of zeolite imidazole framework (ZIF), Co3S4@NiCo2S4 demonstrated excellent electrochemical performance with a specific capacitance of up to 2697.7 F g−1 at 1 A g−1 and cycling stability of 80.5% after 5000 cycles. The covalent organic framework (COF) derived nano carbon, which had undergone secondary calcination and ZnCl2 activation, also exhibited excellent double-layer energy storage performance. Compared to a single calcination, the incredible increase in capacitance was up to 208.5 times greater, reaching 291.9 F g−1 at 1 A g−1 while maintaining ultra-high rate performance (81.0% at 20 A g−1). The hybrid supercapacitor, assembled with Co3S4@NiCo2S4 as the cathode and COF-derived carbon as the anode, exhibited an extremely high energy density (79.7 Wh kg−1 at 693.5 W kg−1) and excellent cyclic stability (maintained 79.3% after 10,000 cycles of 20 A g−1), further explaining the reliable and practical characteristics. This work provided reference for the structural optimization of transition metal sulfides and the high-temperature activation of COF-derived carbon.

Construction of TiO2 on cotton straw deposited on g-C3N4 heterojunction to improve the photocatalytic degradation activity of methylene blue and tetracycline

In this study, agricultural waste cotton stalk was used as biomass carbon source, calcined with TiO2 at a high temperature, deposited in a TiO2 lattice, and used as an electron acceptor to inhibit photogenerated electron recombination. Subsequently, it underwent secondary calcination with g-C3N4 to form a C-TiO2/g-C3N4 composite catalyst. Experimental results showed that the coupling of carbon-doped TiO2 and g-C3N4 accelerated photogenerated electron–hole pairs pair migration, effectively inhibited the recombination of photogenerated carriers, and thus improved the removal efficiency of methylene blue (MB) and tetracycline hydrochloride (TC). Upon irradiation with a 500 W xenon lamp, the degradation rates of MB and TC achieved were 92.6 % and 95.3 % in 90 min, respectively.

Mechanism study of toluene removal using iron/nickel bimetallic catalysts supported on biochar

The present study utilized rice husk biomass as a carrier to synthesize rice husk biochar loaded with iron and nickel. Mono-metallic and bimetallic catalysts were prepared for the removal of toluene as the tar model. The efficiency of the catalysts for the removal of toluene was investigated, and finally, the removal mechanisms of mono-metallic and bimetallic catalysts for toluene were revealed. The experimental results showed that the bimetallic-loaded biochar catalysts had excellent toluene removal performance, which was closely related to the ratio of loaded Fe and Ni. Among them, the catalyst DBC–Fe2.5 %-Ni2.5 % (2.5 wt% iron loading and 2.5 wt% nickel loading) obtained through secondary calcination at 700 °C achieved the highest toluene removal efficiency of 92.76 %. The elements of Fe and Ni in the catalyst were uniformly dispersed on the surface and in the pores of the biochar, and the catalyst had a layered structure with good adsorption. Under the interaction of Fe and Ni, the agglomeration and sintering of Ni were reduced, and the surface acidity of the catalyst was increased, the surface acidity was favorable for toluene removal. The iron‑nickel catalyst did not form significant alloys when calcined at 400 °C, whereas strong metal interactions occurred at 700 °C, resulting in the formation of Fe0.64Ni0.36 alloy and NiFe2O4 alloy. This NiFe alloy had abundant active sites to enhance the catalytic cracking of toluene and provide lattice oxygen for the reaction. Furthermore, the functional groups on the catalyst surface also had an impact on toluene removal. The catalyst prepared in this paper reduces the cost of tar removal, can be applied to the removal of industrial pollutant tars, reduces the pollution of the environment, and provides theoretical guidance and technical reference for the efficient removal of tar.

Rapid removal of ofloxacin with peroxymonosulfate activation process mediated by Co3O4/Sludge-derived biochar composite: Unveiling the enhancement of biochar

In this study, sludge-derived biochar loaded Co3O4 composite (Co3O4@SDBC) were successfully synthesized through cobalt impregnation and secondary calcination of sludge-derived biochar precursors. The experimental results demonstrated that the Co3O4@SDBC catalyst performed exceptionally well for peroxymonosulfate (PMS) activation, with a high degradation efficiency (>99 %) of ofloxacin (OFL) within 10 min under the optimal conditions (a catalyst dose of 0.10 g•L−1, a PMS dose of 0.975 mM and an initial pH = 6.4), and showed good adaptability across a broad pH spectrum, under the interference of the anions and humic acid (HA), as well as in various water matrices. The results of quenching experiments revealed that the non-radical pathway (especially 1O2 and electron transfer) was the dominated reactive ingredients in the PMS activation process induced by Co3O4@SDBC. Notably, the online electrochemical tests and density functional theory (DFT) results indicated the presence of biochar carrier not only effectively lowered the escape of Co ions, while enhanced the steadiness of Co3O4@SDBC, but also accelerated the electron transfer, promoted the adsorption and cleavage of PMS, facilitated the redox cycle between Co(II) and Co(III), reduced the reaction energy barriers simultaneously, thereby making it more favourable for the generation of 1O2. Furthermore, the toxicity assessment suggested that the cumulative toxicity of OFL decreased throughout degradation. Overall, this work mechanistically revealed the enhancement of biochar on the Co3O4@SDBC catalyst, offering a viable method to activate PMS for antibiotic removal and achieving a mutually beneficial strategy for sludge waste resource utilization and environmental remediation.

G-C3N4@CPP/BiOClBr-OV biomimetic fractal heterojunction synergistically enhance carrier dynamics for boosted CO2 photoreduction activity

In recent years, there has been significant interest in generating high-value solar fuels via the photocatalytic reduction of CO2. Nonetheless, its large-scale application is impeded by low energy utilization efficiency and limited photocatalytic activity. This study employed carbonized pomelo peel (CPP), a waste biomass material, to successfully craft a CN@CPP/BOCB-OV ternary heterojunction abundant in N/O vacancy defects through secondary calcination and in-situ growth. The construction of the heterojunction and the emergence of defect-induced donor energy levels create a built-in interface electric field (IEF) and an interfacial electron transmission channel respectively, fortifying the separation and transport of photogenerated electrons. Crucially, following the incorporation of CPP, its distinctive 3D porous and heterojunction bionic flower structures expand the spectral absorption range. Acting as a superior electron acceptor, CPP reinforces the IEF, notably boosting carrier transport efficiency. Simultaneously, it operates as a hub for photothermal synergy and CO2 adsorption activation, achieving multi-site synergistic enhancement of photoreduction CO2 activity. Hence, the CN@CPP/BOCB-OV heterojunction demonstrates a substantial quantitative enhancement in CO2 photoreduction activity. Remarkably, it exhibits the capability to catalyze CO2 reduction even under infrared light excitation, which is of great significance for the cascade utilization of solar energy. Furthermore, employing DFT calculations, we elucidate the electron transfer mechanism at the heterojunction interface and outline potential pathways for photocatalytic CO2 reduction. The combination of waste biomass utilization, heterostructure construction and defect engineering provides a promising strategy for developing efficient heterostructure photocatalysts.

Boosting photocatalytic antibiotic degradation with simultaneous H2O2 production of g-C3N4 by building dual-dragging force for efficient charge separation

Graphitic carbon nitride (g-C3N4) is a promising candidate for photocatalytic antibiotic degradation with simultaneous H2O2 production. However, g-C3N4 suffers from a high charge recombination and insufficient visible-light absorption. Herein, the benzene-ring and cyano groups were successfully grafted onto the surface of g-C3N4 (BCN-ND) by a simple coupling route involving copolymerization and secondary calcination, which provided a dual-dragging force was generated for the directional separation of photogenerated electrons and holes. The benzene-ring establishes a mid-state slightly above the valence band, which results in a dragging force for holes and extends the response of g-C3N4 to visible light. Moreover, the cyano group exhibits a powerful electron-withdrawing capacity, acting as an electron-dragging force and narrowing the intrinsic bandgap. Therefore, BCN-ND exhibits remarkable photocatalytic activity with a sulfamethoxazole degradation percentage of 99.5 % and simultaneous H2O2 production of 62 μmol/L after 80 min of visible light irradiation. This work provides new perspectives for enhancing photocatalytic activity by constructing of a dual-dragging center for oppositely directional charge separation.

Dual Z‐scheme ternary heterojunction photocatalyst with enhanced visible‐light photocatalytic degradation of organic pollutants

AbstractPhotocatalysis technology driven by solar energy is considered to be promising for solving energy crisis and environmental problems. Graphitic carbon nitride has been widely researched in the photocatalysis field due to its suitable band positions, non‐toxicity, easy synthesis, high stability, and low cost. However, the slow separation and rapid recombination of photogenerated carriers, the poor visible light response and the low specific surface area seriously limit the photocatalytic activity of g‐C3N4. Here, firstly, g‐C3N4 nanosheets with a large specific surface area of 152.2 m2 g−1 which provide more surface‐active sites for photocatalysis were prepared by secondary calcination method. Next, MoS2 and metal–organic framework (MIL‐101(Cr)) were tightly bonded on g‐C3N4 nanosheets to form ternary g‐C3N4/MoS2/MIL‐101(Cr) heterojunction photocatalyst. In which, a ternary dual Z‐scheme heterojunction photocatalyst composed of g‐C3N4, MoS2, and MIL‐101(Cr) was constructed to facilitate the separation and the migration of photogenerated charges. At the same time, MoS2 enhanced the visible light response of the ternary photocatalyst. The optimal ternary photocatalyst displayed the highest activity for methyl orange degradation (degradation efficiency of 98% in 60 min) under visible light irradiation. Finally, a photocatalytic mechanism of a dual Z‐scheme electron transfer channel and h+‐·O2− double oxidation sites were proposed and discussed.

S/P co-doped g-C3N4 with secondary calcination for excellent photocatalytic performance

The metal-free and low-cost g-C3N4 has received a lot of attention from researchers as a photocatalyst to solve environmental and energy problems. However, bulk g-C3N4 suffers from limited light absorption, few reactive sites and easy recombination of photogenerated electrons and holes, resulting in unsatisfactory photocatalytic performance. In this study, g-C3N4 nanosheets with excellent photodegradation performance were successfully fabricated by a combination of S/P co-doping and secondary calcination modifications. The modified g-C3N4 could degrade 99.4% rhodamine B (30 mg L−1) in only 4 min, which was 15 times higher than that of pure g-C3N4 due to the synergistic effect of bi-element doping and secondary calcination. Furthermore, experiments using photocatalytic water splitting for hydrogen production have shown different results, demonstrating that the critical factor is different from the photodegradation reaction.This paper provides an effective and feasible novel idea for the modification of g-C3N4.

Morphological and microstructural engineering of Mn-N-C with strengthened Mn-N bond for efficient electrochemical oxygen reduction reaction

Revealing the correlation between the micro–macro structures and active sites of transition metal-nitrogen-carbon (M−N−C) for electrochemical oxygen reduction reaction (ORR) is essential to develop non-precious metal catalyzed fuel cells and metal-air batteries. Herein, Mn-N-C catalysts with various morphologies and microstructures were prepared using Mn2+ coordinated bis(imino)-pyridine-based polymer with N-rich content as a new platform of precursor, which was synthesized via a condensation reaction of 1H-1, 2, 4-Triazole-3, 5-Diamine and 2, 6-Diacetylpyridine. Results demonstrate that morphologies and fine structures (pore structure, N dopants, surface area, and atomic Mn-N bond length, etc.) of Mn-N-C catalysts are strongly dependent on the growth of the specific precursor with and without NaCl as a template and the secondary calcination temperature can further optimize the bond length of Mn-Nx moieties, resulting in significant activity differences between correspondingly derived Mn-N-C catalysts for ORR. Compared to Mn-N-C derived from the synthesized precursor without NaCl, Mn-N-C obtained by the precursor grown directly on NaCl features an ultra-thin nanosheet-like structure with a hierarchical pore distribution and a shorter Mn-N bond, presenting high ORR performance with a half-wave potential of 0.88 V in 0.1 M KOH and a tiny potential loss of 11 mV after 30 K cycles, which is also proved by high-performance practical single Zn-Air battery (139 mW·cm−2) and proton exchange membrane fuel cell (400 mW·cm−2). This work provides a new understanding of the critical role of morphology and Mn-N bonding length of M−N−C for enhancing ORR and a new route of developing non-Fe/Co-based M−N−C catalysts for electrocatalysis.

Insights to PFOS elimination with peroxydisulfate activation mediated by boron modified Fe/C catalysts: Enhancing mechanism of boron and PFOS degradation pathway

In this study, the boron-doped iron-carbon composite (Fe@B/C-2) was prepared via a simple solvothermal and secondary calcination process by using iron metal–organic frameworks (Fe-MOFs) as precursor. The obtained Fe@B/C-2 possessed abundant active sites and low iron ion leaching, and exhibited excellent performance on peroxydisulfate (PDS) activation for efficient PFOS (10 mg/L) degradation (94 %) in 60 min, with 0.2 g/L of catalyst dosage, 1.0 g/L of PDS dosage and at 5.0 of initial pH. The radical scavenging and electron paramagnetic resonance (EPR) tests demonstrated that SO4·− and ·OH were the primary active species during PFOS elimination. Under the attack of these species, PFOS was first transformed into PFOA, followed by a sequential defluorination process, and lastly mineralized into CO2 and F−. Notably, DFT results revealed that Fe species, -BC3/-BC2O structures on the carbon matrix performed crucial roles in PDS activation. The extraordinary catalytic activity of Fe@B/C-2 was attributable to the synergistic effects of Fe nanoparticles and the B-doped on carbon matrix. The doped B not only could activate the inert carbon skeleton and provided more catalytic centers, but also could accelerate the electron transfer efficiency, leading to a boost in PDS decomposition.

Oxygen-tolerant and recyclable graphitic carbon nitride (g-C3N4) catalyzed photo-induced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT) without any additives

The existing photo-induced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT) systems using g-C3N4 as catalyst are complicated and often require modification of g-C3N4 or additives as co-catalyst. Herein, we propose an economical g-C3N4 catalyzed PET-RAFT polymerization without any additives. The good catalytic ability of g-C3N4 is attributed to the fact that the thermal exfoliation by secondary calcination increases the specific surface area and thus exposes more photocatalytic active sites. The g-C3N4 catalyzed PET-RAFT polymerizations of methyl methacrylate were successfully carried out under blue LEDs. The faster polymerization rates without prior deoxygenation showed good oxygen-tolerant. The g-C3N4 can be easily recovered after polymerization and cycled at least seven times with little loss of catalytic performance.

Layered FeMo2S4-packed hexagonal nitrogen-doped carbon microsheets embedded with Fe3C nanoparticles for efficient electrocatalytic oxygen evolution reaction

The design of efficient, low-cost non-noble metal oxygen evolution reaction (OER) catalysts has attracted considerable attention. Fe3C sites have excellent catalytic effects arising from their high electrical conductivity and numerous active sites. Moreover, the high–valence state of molybdenum significantly enhances the electrochemical performance of electrocatalysts. Herein, we propose a design strategy through which hexagonal Fe3C/NC microsheets can be successfully synthesised using a self-template. This strategy also demonstrates how the surfaces of hexagonal microsheets can be covered with FeMo2S4 nanosheets with active sites via hydrothermal and secondary calcination. FeMo2S4–Fe3C/NC exhibits outstanding catalytic performance, achieving a current density of 10 mA cm−2 with an overpotential of only 243 mV, Tafel slope of 32 mV dec−1, and excellent stability for up to 50 h. The number of active sites on the catalyst surface can be increased by introducing Mo and S, which effectively change the structure of the electronic environment. This study presents a new method of designing simple and efficient non-precious-metal catalysts with excellent performance for use in OER.

Facile synthesis of ultrathin g-C3N4 nanosheets modified with N-doped carbon dots: Enhanced photocatalytic hydrogen production activity and mechanism insight

In this study, nitrogen-doped carbon dots (NCDs) modified ultrathin carbon nitride (g-C3N4) nanosheets were synthesized by a simple secondary calcination method, which realizes efficient photocatalytic hydrogen production. The secondary calcination process can not only thermally exfoliate g-C3N4 into ultrathin nanosheets, but also uniformly anchor NCDs (∼3 nm) on the surface of g-C3N4. The photocatalytic results manifested that a very small amount of NCDs (0.5 wt%) loading on g-C3N4 could achieve a high photocatalytic hydrogen production rate (5.21 mmol g−1 h−1). The reasons for the enhanced photocatalytic activity were analyzed. The ultrathin g-C3N4 nanosheets facilitated the migration of photogenerated carriers. Moreover, NCDs/g-C3N4 exhibited enhanced visible light absorption owing to the up-conversion fluorescence effect of NCDs and the narrow band gap caused by the decoration of NCDs. Furthermore, NCDs as electron acceptors can promote carrier separation. This combination strategy provides a basis for the synthesis of inexpensive, metal-free, and efficient carbon-based photocatalysts.

Perovskite-Like Strontium Bismuth Oxyhalides: Synthesis, Characterisation, Photocatalytic Activity and Degradation Mechanism

Recent studies have demonstrated that bismuth oxyhalides with a 2D structure inhibit the recombination of electron–hole pairs. Further, perovskite-like strontium bismuth-based compounds with a special layered Sillen X1 structure have shown potential for use as effective visible-light photocatalysts. Here, a series of strontium bismuth oxyhalide composites were prepared under different calcination conditions. The sample compositions were controlled by modulating the calcination temperature and the secondary calcination time. The synthesised catalysts were characterised by various techniques to identify the product compositions. Under visible-light irradiation, the degradation efficiencies and photocatalytic activities of the different catalysts towards rhodamine B (RhB) and 2-hydroxybenzoic acid (2-HBA) were measured via UV–Vis PDA and electron paramagnetic resonance analyses. To explore the degradation mechanism, scavengers were utilised to detect the radicals produced in the photodegradation test. SrBiO2Cl exhibited the best RhB degradation efficiency, of 0.0685 h−1, and SrBiO2Br exhibited a rate of 0.0984 h−1. At 25 °C and 1 atm, the CO2–CH4 photocatalytic conversion efficiencies of the optimised SrBiO2Cl and SrBiO2Br samples increased to 0.037 and 0.053 μmol g−1 h−1, respectively. The findings confirm that the catalysts are highly recyclable and effective for environmental remediation, achieving the objectives of green chemistry.

Lattice-strained Pt nanoparticles anchored on petroleum vacuum residue derived N-doped porous carbon as highly active and durable cathode catalysts for PEMFCs

High cost and poor durability of Pt-based cathode catalysts for oxygen reduction reaction (ORR) severely hamper the popularization of proton exchange membrane fuel cells (PEMFCs). Tailoring carbon support is one of effective strategies for improving the performance of Pt-based catalysts. Herein, petroleum vacuum residue was used as carbon source, and nitrogen-doped porous carbon (N-PPC) was synthesized using a simple template-assisted and secondary calcination method. Small Pt nanoparticles (Pt NPs) with an average particles size of 1.8 nm were in-situ prepared and spread evenly on the N-PPC. Interestingly, the lattice compression (1.08%) of Pt NPs on the N-PPC (Pt/N-PPC) was clearly observed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which was also verified by the shift of (111) crystal plane of Pt on N-PPC to higher angles. The X-ray photoelectron spectroscopy (XPS) results suggest that the N-PPC support had a strong effect on anchoring Pt NPs and endowing surface Pt NPs with lowered d band center. Thus, the Pt/N-PPC as a catalyst simultaneously boosted the ORR activity and durability. The specific activity (SA) and mass activity (MA) of the Pt/N-PPC at 0.9 V reached 0.83 mA cm−2 and 0.37 A mgPt−1, respectively, much higher than those of the commercial Pt/C (0.21 mA cm−2 and 0.11 A mgPt−1) in 0.1 M HClO4. The half-wave potential (E1/2) of Pt/N-PPC exhibited only a minimal negative shift of 7 mV after 30,000 accelerated durability tests (ADT) cycles. More importantly, an H2–O2 fuel cell with a Pt/N-PPC cathode achieved a power density of 866 mW cm−2, demonstrating that the prepared catalyst has a promising application potential in working environment of PEMFCs.

Alkali metal doped crystalline g-C3N4 with an enriched cyano group for visible-light photocatalytic degradation of methylamine.

In this study, alkali-metal-doped crystalline g-C3N4 with an enriched cyano group was synthesized using the molten salt method and used for the visible-light photocatalytic degradation of methylamine (MA), a common organic amine compound with a low odor threshold. Different types and proportions of melting salts (Li, K, and Na) were added during secondary calcination to regulate the morphology, crystallinity, and surface defects of graphitic carbon nitride (g-C3N4). With molten salt treatment matched the melting point of the binary salt system, a cyano group and alkali metal co-doped crystalline g-C3N4 with a high surface area and good crystallinity were prepared. Co-decorating the alkali metal and cyano groups on crystalline g-C3N4 facilitated the adsorption of MA, realized an excellent photo-charge transfer efficiency, and generated more superoxide radicals. Compared with pristine g-C3N4 (PCN), the apparent rate constant of LiK15 : 5-CCN for the degradation of MA increased by 10.2 times and the degradation efficiency of 1000 ppm MA gas was 93.1% after 90 min of irradiation with visible light, whereas the degradation efficiency of PCN was 19.2%.