Indoor HCHO Research Articles

Efficient degradation of methylene blue and HCHO by nonmetallic B-doped g-C3N5: activity and mechanism analysis

To solve the pollution of natural water bodies by organic dyes and the exceeding of indoor HCHO standards caused by renovation, the study realized the band gap modulation of g-C3N5, a novel semiconductor photocatalytic material, by using H3BO3 as a source of nonmetallic B. The prepared B/g-C3N5 has shown excellent photocatalytic performance and stability for organic dye degradation in water bodies and indoor HCHO removal. The degradation rate of methylene blue (MB) reached 95% in 60 min of visible light, and the removal rate of HCHO reached 96.3% in 180 min of visible light. The MB and HCHO were efficiently degraded to small molecule inorganic compounds such as CO2 and H2O under the oxidation of active groups such as ·O2 − and h+. The doping of nonmetallic B realizes the efficient separation of e−-h+ of g-C3N5, improve the absorption performance of visible light, and broaden the spectral range significantly. The modulation of the g-C3N5 band gap provides a potential application scenario for the development of novel photocatalytic materials.

ZnMn2O4‐BiVO4 as Photocatalyst for Degradation of Gaseous HCHO Using Daylight

AbstractFormaldehyde (HCHO) is a common indoor air pollutant. Due to its proven carcinogenicity, reducing indoor HCHO levels is a significant issue. In this study, a composite material consisting of zinc manganese oxide and BiVO4 was used as a photocatalyst for HCHO degradation. ZnMn2O4‐BiVO4 has efficient photocatalytic performance, wide application areas, high stability, and low‐cost advantages, making the substance a potentially useful photocatalyst that can be applied in fields such as energy conversion and environmental protection. BiVO4 was prepared by a hydrothermal method. It was further compounded with zinc manganese oxide to form composite as catalysts of different wt % ratios for photodegradation of HCHO using a fluorescent lamp as light source. The samples were characterized by using XRD, UV‐visible spectrometer, TEM, SEM, and photoluminescence spectrometry. The experimental data showed that 5.0 wt % zinc manganese oxide‐BiVO4 as catalyst had the highest HCHO degradation rate. The release of carbon dioxide and water increased the irradiation time. The degradation rate of HCHO was higher than that achieved with commercially available titanium oxide. The highest HCHO degradation rate was 66 % within 4 h.

Lattice-confined Ag over MnCoLDH accelerated catalytic oxidation of formaldehyde at ambient temperature: The novel pathway with different oxygen species

Catalytic oxidation of formaldehyde (HCHO) at ambient temperature represents a cost-effective and efficient strategy for indoor HCHO removal. Although precious metal-based catalysts have been considered practical for oxidizing gaseous HCHO indoors, the limited activity of Ag-based catalysts can be attributed to their typical +1 and 0 valence states, as well as their single electron transport pathway. This characteristic impedes the reestablishment of the low state during oxygen activation, thereby resulting in catalyst deactivation. The present study successfully incorporated Ag atoms into manganese-cobalt layered double hydroxide (MnCoLDH) through doping, resulting in the development of a catalyst that exhibited complete formaldehyde oxidation activity at 30 °C. Lattice-confined Ag enables continuous activation of oxygen, while LDH facilitates the sustained provision of surface hydroxyl groups. The roles and mechanisms of surface hydroxyl groups, adsorbed oxygen, and lattice oxygen in the oxidation of formaldehyde were investigated using in-situ DRIFTS. By comparing Ag with the impregnation method, the confinement of Ag within the lattice enables continuous activation of oxygen. This study presents a viable strategy for designing efficient catalysts for volatile organic compounds (VOCs) removal by utilizing active lattice oxygen species.

Three-dimensional Ni foam supported Pt/NiFe LDH catalyst with enhanced oxygen activation for room-temperature formaldehyde oxidation

Room-temperature catalytic oxidation of formaldehyde (HCHO) has been extensively investigated due to its high efficiency, convenience, and environmental friendliness. Herein, nickel-iron layered double hydroxide (NiFe LDH) nanosheets were synthesized in-situ on a nickel foil (NF) using a facile one-step hydrothermal method, followed by the deposition of ultra-low content (0.069 wt%) of Pt nanoparticles through NaBH4 reduction. The resulting three-dimensional (3D) hierarchical Pt/NiFe-NF catalyst exhibited exceptional activity for the complete decomposition of formaldehyde to carbon dioxide (CO2) at room temperature (∼95 % conversion within 1 h), as well as remarkable cycling stability. The 3D porous structure of Pt/NiFe-NF provides fast transport channels for the diffusion of gas molecules, making the active catalyst surfaces more accessible. Moreover, abundant hydroxyl groups in NiFe LDH serve as adsorption centers for HCHO molecules to form dioxymethylene (DOM) and formate intermediates. Furthermore, electronic interactions between NiFe LDH and Pt enhance the adsorption and activation of O2 on Pt surfaces, leading to the complete decomposition of intermediates into non-toxic products. This work presents new insights into the design and preparation of Pt-based 3D hierarchical catalysts with surface-rich hydroxyl groups for the efficient removal of indoor HCHO.

Synergistic Effect of ZIF-8 and Pt-Functionalized NiO/In2O3 Hollow Nanofibers for Highly Sensitive Detection of Formaldehyde.

A rapid and accurate monitoring of hazardous formaldehyde (HCHO) gas is extremely essential for health protection. However, the high-power consumption and humidity interference still hinder the application of HCHO gas sensors. Hence, zeolitic imidazolate framework-8 (ZIF-8)-loaded Pt-NiO/In2O3 hollow nanofibers (ZPNiIn HNFs) were designed via the electrospinning technique followed by hydrothermal treatment, aiming to enable a synergistic advantage of the surface modification and the construction of a p-n heterostructure to improve the sensing performance of the HCHO gas sensor. The ZPNiIn HNF sensor has a response value of 52.8 to 100 ppm HCHO, a nearly 4-fold enhancement over a pristine In2O3 sensor, at a moderately low temperature of 180 °C, along with rapid response/recovery speed (8/17 s) and excellent humidity tolerance. These enhanced sensing properties can be attributed to the Pt catalysts boosting the catalytic activity, the p-n heterojunctions facilitating the chemical reaction, and the appropriate ZIF-8 loading providing a hydrophobic surface. Our research presents an effective sensing material design strategy for inspiring the development of cost-effective sensors for the accurate detection of indoor HCHO hazardous gas.

Photocatalytic oxidation of formaldehyde under visible light using BiVO4-TiO2 synthesized via ultrasonic blending.

Formaldehyde (HCHO) is one of the primary indoor air pollutants, and efficiently eliminating it, especially at low concentrations, remains challenging. In this study, BiVO4-TiO2 catalyst was developed using ultrasonic blending technology for the photocatalytic oxidation of low-level indoor HCHO. The crystal structure, surface morphology, element distribution, and active oxidation species of the catalyst were examined using XRD, SEM, TEM, UV-Vis, EDS, and ESR techniques. Our results demonstrated that the BiVO4-TiO2 catalyst, prepared by ultrasonic blending, exhibited good oxidation performance and stability. The HCHO concentration reduced from 1.050 to 0.030mg/m3 within 48h, achieving a removal rate of 97.1%. The synergy between BiVO4 and TiO2 enhanced the efficiency of separating photogenerated carriers and minimized the likelihood of recombination between photogenerated electrons and holes. Additionally, this synergy significantly enhanced the presence of hydroxyl radicals (·OH) on the catalyst, resulting in an oxidation performance superior to that of either BiVO4 or TiO2. Our research offers valuable insights for the development of new photocatalysts to address HCHO pollution.

A facile cellulose finishing strategy through in-situ growth of sliver-doped manganese dioxide assisted by amine-quinone for improving indoor living quality

Nowadays, various harmful indoor pollutants especially including bacteria and residual formaldehyde (HCHO) seriously threaten human health and reduce the quality of public life. Herein, a universal substrate-independence finishing approach for efficiently solving these hybrid indoor threats is demonstrated, in which amine-quinone network (AQN) was employed as reduction agent to guide in-situ growth of Ag@MnO2 particles, and also acted as an adhesion interlayer to firmly anchor nanoparticles onto diverse textiles, especially for cotton fabrics. In contrast with traditional hydrothermal or calcine methods, the highly reactive AQN ensures the efficient generation of functional nanoparticles under mild conditions without any additional catalysts. During the AQN-guided reduction, the doping of Ag atoms onto cellulose fiber surface optimized the crystallinity and oxygen vacancy of MnO2, providing cotton efficient antibacterial efficiency over 90 % after 30 min of contact, companying with encouraging UV-shielding and indoor HCHO purification properties. Besides, even after 30 cycles of standard washing, the Ag@MnO2-decorated textiles can effectively degrade HCHO while well-maintaining their inherent properties. In summary, the presented AQN-mediated strategy of efficiently guiding the deposition of functional particles on fibers has broad application prospects in the green and sustainable functionalization of textiles.

The Relationship between Mechanical Ventilation, Indoor Air Quality Classes, and Energy Classes in a Romanian Context

Nowadays, indoor air quality (IAQ) and the energy performance of buildings are two main scientific and technical challenges because they are in direct connection with human health and the depletion of energy resources. In this study, we analyzed the influence of an outdoor air flow introduced through a mechanical ventilation system, focusing on the two aforementioned topics. A standardized ventilation rate (25 m3/h/person) led to an increase in the indoor O3 concentration (from 5 μg/m3 to 50 μg/m3) and, simultaneously, to a decrease in the indoor CO2 concentration (from 2000 mg/m3 to 800 mg/m3), a decrease in the PM2.5 concentration (from 300 μg/m3 to 150 μg/m3), and the maintenance of a constant indoor HCHO concentration. In our study, a new, single indoor air quality index, IIAQ, is proposed. This new index presents different implications: on the one hand, it has the ability to simultaneously take into account several pollutant species, and on the other hand, it can prioritize the ventilation strategy that responds to the extreme values of a certain pollutant. Moreover, indoor air quality classes were elaborated, similar to energy classes. The possibility of using this new index simultaneously with energy consumption may lead to ventilation strategies that are adaptative to dynamic outdoor pollutant concentrations.

Enhanced and Sustainable Removal of Indoor Formaldehyde by Naturally Porous Bamboo Activated Carbon Supported with MnOx: Synergistic Effect of Adsorption and Oxidation

Novel bamboo activated carbon (BAC) catalysts decorated with manganese oxides (MnOx) were prepared with varying MnOx contents through a facile one-step redox reaction. Due to the physical anchoring effect of the natural macropore structure for catalyst active components, homogeneous MnOx nanoparticles (NPs), and high specific surface area over catalyst surface, the BAC@MnOx-N (N = 1, 2, 3, 4, 5) catalyst shows encouraging adsorption and catalytic oxidation for indoor formaldehyde (HCHO) removal at room temperature. Dynamic adsorption and catalytic activity experiments were conducted. The higher Smicro (733 m2/g) and Vmicro/Vt (82.6%) of the BAC@MnOx-4 catalyst could facilitate its excellent saturated and breakthrough adsorption capacity (5.24 ± 0.42 mg/g, 2.43 ± 0.22 mg/g). The best performer against 2 ppm HCHO is BAC@MnOx-4 catalyst, exhibiting a maximum HCHO removal efficiency of 97% for 17 h without any deactivation as RH = 0, which is higher than those of other MnOx-based catalysts. The average oxidation state and in situ DRIFTS analysis reveal that abundant oxygen vacancies on the BAC@MnOx-4 catalyst could be identified as surface-active sites of decomposing HCHO into the intermediate species (dioxymethylene and formate). This study provides a potential approach to deposit MnOx nanoparticles onto the BAC surface, and this hybrid BAC@MnOx material is promising for indoor HCHO removal at room temperature.

Functional graphitic carbon nitride/hydroxyapatite heterojunction for robust formaldehyde removal at ambient temperature

Ambient-temperature catalytic removal of formaldehyde (HCHO) hazard has been currently reckoned as a practicable and promising approach for abating indoor HCHO which severely haunts the human’s health. Catalyst with high-effectiveness and low-cost is a pivotal parameter determining the reliability and availability of this strategy. Herein, bifunctional graphitic carbon nitride/hydroxyapatite heterostructures (g-C3N4/HAP) were developed for indoor HCHO removal at ambient temperature. The optimal catalyst (g-C3N4/HAP-20) displayed enhanced HCHO removal efficiency of 36.6% and conversion (into CO2) efficiency of 28.4% within 2 h, compared with g-C3N4 (18.0% and 24.0%) and HAP (36.2% and ∼ 0%). Indoor fluorescent light accelerated HCHO elimination and its subsequent decomposition into CO2 over g-C3N4/HAP-20, delivering a HCHO removal efficiency of 82.7% and conversion efficiency of 100% within 2 h. Various characterizations and theoretical calculation reveal that g-C3N4/HAP possessed superoxide radicals and unpair electrons which were responsible for HCHO removal at ambient temperature; and a S-scheme heterostructure remarkably benefited the charge transfer and the photogenerated carriers’ separation, and consequently upgraded HCHO catalytic oxidation under indoor fluorescent-light illumination. This work offers a potent way to construct noble-metal free advanced catalysts with multi-functionality for indoor pollutant purification.

Efficient HCHO oxidation at room temperature via maximizing catalytic sites in 2D coralloid δ-MnO2@GO

Airborne formaldehyde (HCHO) in indoor environments causes serious health problems and needs to be efficiently eliminated. However, the efficient and stable catalytic oxidation of HCHO can be hardly achieved at room temperature over transition metal oxides due to the limited exposure of active sites. Herein, δ-MnO2@GO catalysts were originally synthesized via a facile in situ growth of δ-MnO2 on the trace graphene oxide (GO) substrate (1%) and stably exhibited nearly 100% HCHO elimination at room temperature. δ-MnO2@GO showed the unique 2D coralloid structure with uniformly dispersed δ-MnO2 nanorod on planar-structured GO, which greatly enhanced the exposure of catalytic sites and mass transfer of reactants. The abundant surface reactive oxygen species (ROS) and hydroxyl (-OH) groups were rapidly generated from the activation of O2 and surface-adsorbed water over highly exposed catalytic sites. The ROS and -OH groups cooperated well cooperated to maintain the exceptional catalytic activity and stability towards HCHO degradation. In-situ DRIFTS results showed that catalytic HCHO oxidation predominantly follows the Langmuir-Hinshelwood (L-H) mechanism over the δ-MnO2@GO. This study presents a simple yet effective strategy for maximizing exposure to catalytic active sites and rational design of efficient catalysts for indoor HCHO elimination.

Exposure of Elderly People to Indoor Air Pollutants in Wanxia Nursing Home

The elderly residing in nursing homes are typically more advanced in age, have more health issues, and spend more time indoors than other elderly people. This study explored the indoor air quality in the Wanxia nursing home, the largest private nursing home in Chengdu, China, based on long-term measurement data. Air pollutant sensors measured the level of air pollution in the Wanxia nursing home from March 2021 to February 2022. This study obtained several important results: (1) The indoor air quality index (IAQI) of the Wanxia nursing home was at a low pollution level in spring, summer, and autumn, and at a moderate pollution level in winter. PM concentration played the most important role in determining indoor air quality; (2) During winter, the 24 h mean indoor concentrations of PM2.5 and PM10 were close to or even exceeded the standard limits. During winter and summer nights, indoor CO2 levels were very close to or greater than 1000 ppm. During spring and summer nights, the indoor TVOC concentrations exceeded the limit (0.45 mg/m3); (3) Apart from HCHO concentrations in autumn, the levels of other indoor air pollutants were significantly influenced by their outdoor levels. In addition, the seasonal indoor/outdoor (I/O) ratios of CO2 and TVOCs exceeded 1; and (4) Indoor CO2 levels were closely related to indoor temperature (Ta) and relative humidity (RH) in each season. PM10 concentration correlated with Ta and RH in summer, while PM2.5 concentration did not correlate with Ta and RH in winter. The indoor TVOC level positively correlated with RH. Lastly, the indoor HCHO level was minimally influenced by changes in Ta and RH. Due to the above results, this study proposes targeted strategies for improving indoor air quality in nursing homes.

Core-dual-shell structure MnO2@Co–C@SiO2 nanofiber membrane for efficient indoor air cleaning

Developing cost-effective and high-efficient air purification materials for enhancing the indoor air quality has been an ongoing concern. Herein, MnO2/Co–C catalyst layers were wrapped on SiO2 nanofiber by a combination of thermal pyrolysis and redox reaction method to prepare catalytic membranes (MCCS-x) for the efficient purification of indoor PM and HCHO. The core-dual-shell structure maintains the pore structure of the membrane, providing high gas permeability of 670 m3·m−2·h−1·kPa−1. Owing to the introduction of MnO2/Co–C enhanced the capture of PM, the optimized MCCS-2 exhibits high filtration efficiency of PM0.3 and PM2.5 (99.60% and 99.99%) with a low pressure drop (<80 Pa). In addition, MCCS-2 achieves 100% HCHO removal efficiency at room temperature due to its large specific surface area, high redox property and abundant Mn4+ and oxygen species. The appropriate proportion of Mn/Co bimetallic sites synergy inhibits the formation of formate and carbonate intermediate species, thus MCCS-2 possesses excellent long-term catalytic stability than contrast sample (MCCS-3 and MS). This work demonstrates a new approach for the fabrication of high-performance catalytic membrane materials for indoor air purification.

HCHO oxidation over the δ-MnO2 catalyst: Enhancing oxidative activities of surface lattice oxygen and surface adsorbed oxygen by weakening Mn-O bond

The usages of HCHO in construction and decoration materials lead to serious indoor air pollution, removing the indoor HCHO to improve air quality is urgently required. In this work, we developed a new procedure to synthesis ultra-thin nanosheet δ-MnO2 without using traditional templates. The Mn-O bond was much weaker in the ultra-thin nanosheet δ-MnO2 than those in the β- and γ-MnO2. As a consequence, surface oxygen lattice of the δ-MnO2 was the most removable, generating the most oxygen vacancy on the surface. The oxidative ability of the lattice oxygen was the most enhanced, active surface adsorbed oxygen species were the most present on the δ-MnO2 surface. These contributed to an unexpected performance that 100 ppm HCHO was fully oxidized at 35–45 °C depending on the relative humidity between 10 and 50% at high space velocity of 300 L/(gh). When compared with HCHO oxidation performance of MnO2 in literatures, the current ultra-thin nanosheet δ-MnO2 lists the most active HCHO oxidation catalyst as regards to the lowest activation energy, the lowest temperature of full HCHO conversion and the highest rate of HCHO oxidation, giving the most promising potential application for practical indoor HCHO elimination.

Hierarchical Pt/NiCo2O4 nanosheets decorated carbon nanofibers for room-temperature catalytic formaldehyde oxidation

Room-temperature catalytic formaldehyde (HCHO) oxidation is regarded as the most promising way for constant and oxidative removal of indoor HCHO. Herein, carbon nanofibers (CNF) with three-dimensional (3D) interconnection network structure decorated with Pt/NiCo2O4 alloy nanosheets (Pt/NiCo2O4/CNF) were fabricated in-situ to catalyze the oxidation of HCHO at ambient temperature. The presence of CNF helps to inhibit the aggregation of NiCo2O4 nanosheets, expose more active sites and form a hierarchically porous structure, which is conducive to the dispersion of platinum nanoparticles (NPs) and the diffusion of reactants. Besides, oxygen vacancies from Pt-loading process ensure abundant active oxygen species, which are beneficial to HCHO oxidation. Moreover, CNF with microporous structure can strongly adsorb HCHO, rapidly reduce the concentration of HCHO in air and increase its concentration near Pt/NiCo2O4, thus accelerating the formaldehyde oxidation reaction. At Pt content as low as 0.5 wt%, Pt/NiCo2O4/CNF exhibits superior HCHO oxidation activity, and conversion of 92.4% can be achieved within 60 min due to the combination of adsorption and oxidation. This work may shed light on fabricating CNF-based 3D catalysts for the practical application of indoor HCHO elimination.

Unveiling the Position Effect of Ce within Layered MnO2 to Prolong the Ambient Removal of Indoor HCHO.

The position of Ce doping has a significant effect on ambient HCHO storage and catalytic oxidation on layered MnO2. By associating structure and performance, it is unveiled that doping Ce into the in-layered lattice of MnO2 is favorable to the generation of high-valence Mn cations, enhancing the oxidizing ability and capacity, but an opposite influence is displayed by interlayered Ce doping. From the aspect of energy minimization calculated by DFT, in-layered Ce doping is also recommended due to the decreased energies for molecule adsorption and oxygen vacancy formation. As a result, in-layered Ce-doped MnO2 displays exceptional activity in catalyzing the deep oxidation of HCHO and a fourfold higher capacity of ambient HCHO storage than pristine MnO2. The optimal oxide is combined with electromagnetic induction heating to complete the "storage-oxidation" cycle as a promising approach absolutely depending on non-noble oxides and household appliances to realize the long-acting removal of indoor HCHO at room temperature.

Adsorptivity and kinetics for low concentration of gaseous formaldehyde on bamboo-based activated carbon loaded with ammonium acetate particles

The highly promising formaldehyde (HCHO)-removing materials are essential for eliminating interior pollution to safeguard the public's health with increasing indoor HCHO contamination situations being recorded on a global scale. In the paper, bamboo charcoal (BC) was activated with boric acid to prepare bamboo-based activated carbon (BAC), and then impregnated with ammonium acetate solution to successfully develop porous adsorbent with ammonium acetate particles (N/BAC), which was applied to remove low concentration of HCHO at room temperature. The adsorption performance for HCHO was systematically investigated while the surface chemical properties and microstructure of the as-prepared adsorbents were described and analyzed. The specific surface area, total pore volume and microporous volume of N/BAC sample were 240.09 m2/g, 0.27 cm3/g and 0.12 cm3/g, which increased by 42.40 m2/g, 0.15 cm3/g and 0.03 cm3/g compared with BAC sample, respectively. The specific surface area and the microporous volume, as well as the content of oxygen- and nitrogen-containing functional groups of N/BAC sample were augmented by contrast with other samples, and numerous ammonium acetate particles were present on the surface. Precisely because of this, the N/BAC sample exhibited a high removal rate of 98.89%, which was 18.38% greater than that of BAC sample. A superior correlation coefficient (0.9999) from the experimental values of the kinetics and the fitted values of the pseudo-second-order kinetic model demonstrated that the adsorption process of HCHO on N/BAC sample was physical-chemical combined adsorption. The adsorption of HCHO on N/BAC sample was investigated under different humidity, and the results showed that the adsorbent yet had excellent adsorption capacity (87.93%) under RH 75%. Moreover, the N/BAC sample was renewable, and the removal rate still reached 82.81% after five cycles of regeneration. Therefore, the as-prepared adsorbent is an effective, economical and sustainable material, and could be used to remove HCHO from real contaminated indoor air.

Ag-promoted Cr/MnO2 catalyst for catalytic oxidation of low-concentration formaldehyde at room temperature.

As one of the significant pollutants in indoor air, formaldehyde (HCHO) has attracted increasing attention due to its negative effects on human health. Thus, to reduce formaldehyde pollution, herein, an Ag-promoted Cr/MnO2 catalyst (Ag/Cr/MnO2) was obtained via a hydrothermal-calcination method, which was employed for the catalytic oxidation of low-concentration indoor HCHO (∼1 ppm) at room temperature. The Ag/Cr/MnO2 catalyst eliminated approximately 98.62% HCHO within 14 h and maintained a high removal efficiency continuously under the dynamic test conditions. Furthermore, the catalyst exhibited good recycling stability and outstanding activity in a humid environment. Different characterization techniques were utilized to determine the physicochemical properties that contribute to improving the catalytic performance. The Ag substance contained metallic Ag (Ag0) as the main component and some Ag2O, and the Ag0 particles provided ample active sites for the catalytic oxidation of HCHO. Besides, the incorporation of Ag increased the reducibility of the catalyst and the content of Mn4+, Cr6+ and oxygen vacancies. The abundant active sites, high reducibility, rich Mn4+, Cr6+, oxygen vacancies, and surface lattice oxygen species, and the powerful interaction between Cr/MnO2 and Ag were the reasons for the splendid catalytic capability for HCHO by the Ag/Cr/MnO2 catalyst. In conclusion, the Ag/Cr/MnO2 catalyst can be a promising catalyst to degrade HCHO with practical application significance.

Pt/NiCo2O4 nanowire arrays on Ni foam as catalysts for efficient formaldehyde oxidation at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is a low-cost and efficient solution for indoor HCHO removal. In this work, NiCo2O4 nanowires were in-situ synthesized on nickel foam (NF) by a simple hydrothermal reaction and then decorated with platinum nanoparticles (NPs). The Pt/NiCo2O4-NF catalyst exhibited excellent HCHO oxidation capacity at ambient temperature, realizing a conversion rate of 90 % within 60 min. The nickel foam substrate prevents the aggregation of NiCo2O4 nanowire arrays. It also enables the growth of large-area and aligned nanowires, contributing to the uniform dispersion of Pt NPs. Moreover, due to the unique redox property and high reactivity of NiCo2O4, numerous surface oxygen vacancies and active oxygen species are generated together with Pt by NaBH4 reduction, which is beneficial to the adsorption and oxidation of HCHO. Moreover, the hierarchical macro-/mesoporous structure of Pt/NiCo2O4-NF facilitates the diffusion of gaseous reactants and provides easily accessible active sites. In contrast with nanosized catalysts, the three-dimensional (3D) Pt/NiCo2O4-NF catalyst possesses high machinability and practicability. This work may shed light on the fabrication of 3D hierarchical catalysts for oxidative HCHO removal and indoor air purification.

Synergetic palladium-modulated and B/N Lewis pair-functionalized flocculent carbon fibres as robust catalyst: Mechanism insight for indoor HCHO decomposition

In this study, electron-deficient boron and electron-rich nitrogen are designed as the B/N Lewis pair to capture HCHO, and in next step the adsorbed HCHO is degraded into CO2 and H2O (mineralization efficiency 97 %) via the Fenton-like O2 activation and generation singlet oxygen (1O2), superoxide radicals (•O2−) and hydroxyl radicals (•OH) derived from the interaction between palladium nanoparticles and oxygen molecules. Experimental data and theoretical calculations reveal the optimal path as follows: HCHO + OH* (•OH) → HCHOOH* → HCOOH + OH* (•OH) → CHO2* + O* (1O2 and •O2−) → CO2, which correspond to the lowest energy barrier for elementary reaction. This study demonstrates a strong catalytic HCHO oxidation process and a new insights into exploiting synergetic palladium-modulated and B/N Lewis pair-functionalized flocculent carbon fibres for room-temperature HCHO decomposition.