Conjugated microporous poly(aniline)s for removal of low-concentration formaldehyde

Surface Structure Analysis and Formaldehyde Removal Mechanism of Lotus Shell Biochar: An Experimental and Theoretical Perspective

The adsorption of gaseous HCHO by raw lotus shell biochar carbonized at 500, 700, and 900 °C from the perspective of its internal crystal structure and surface functional groups was investigated by an integrated approach of experiments and density functional theory calculations. The results showed that lotus shell biochar carbonized at 700 °C had the best adsorption effect at a HCHO concentration of 10.50 ± 0.30 mg/m³, with an adsorption removal rate of 87.64%. The HCHO removal efficiency by lotus shell biochar carbonized at 500 and 900 °C was determined to be 80.96 and 83.07%, respectively. The HCHO adsorption on lotus shell biochar carbonized at 700 °C conformed to pseudo-second-order kinetics and was predominantly controlled by chemical adsorption. The Langmuir isotherm was the underlying mechanism for the monomolecular layer adsorption with a maximum adsorption capacity of 0.329 mg/g. The density functional theory calculations revealed that the adsorption of HCHO on the surface of CaCO₃ and KCl in lotus shell biochar carbonized at 700 °C was a chemical adsorption process, with adsorption energies ranging from -64.375 to -87.554 kJ/mol. The strong interaction between HCHO and the surface was attributed to the electron transfer from HCHO to the surface, facilitated by metal atoms (Ca or K) and the oxygen atoms of HCHO. The carboxyl group on the surface of lotus shell biochar carbonized at 700 °C was identified as the key functional group responsible for HCHO adsorption. This study advanced our understanding of the environmental functions of inorganic crystals and surface functional groups in raw biochar and will enable the further development of biochar materials in environmental applications.

High Efficiency of Formaldehyde Removal and Anti-bacterial Capability Realized by a Multi-Scale Micro-Nano Channel Structure in Hybrid Hydrogel Coating Cross-Linked on Microfiber-Based Polyurethane

Inspired by the transpiration in the tree stem having a vertical and porous channel structure, high efficiency of formaldehyde removal is realized by the multi-scale micro-nano channel structure in a hybrid P(AAm/DA)-Ag/MgO hydrogel coating cross-linked on microfiber-based polyurethane. The present multi-scale channel structure is formed by a joint effect of directional freezing and redox polymerization as well as nanoparticles-induced porosity. Due to the large number of vertically aligned channels of micrometer size and an embedded porous structure of nanometer size, the specific surface area is significantly increased. Therefore, formaldehyde from solution can be rapidly adsorbed by the amine group in the hydrogels and efficiently degraded by the Ag/MgO nanoparticles. By only immersing in formaldehyde solution (0.2 mg mL^-1) for 12 h, 83.8% formaldehyde is removed by the hybrid hydrogels with a multi-scale channel structure, which is 60.8% faster than that observed in hydrogels without any channel structure. After cross-linking the hybrid hydrogels with a multi-scale channel structure to microfiber-based polyurethane and exposing to the formaldehyde vapor atmosphere, 79.2% formaldehyde is removed in 12 h, which is again 11.2% higher than that observed in hydrogels without any channel structure. Unlike the traditional approaches to remove formaldehyde by the light catalyst, no external conditions are required in our present hybrid hydrogel coating, which is very suitable for indoor use. In addition, due to the formation of free radicals by the Ag/MgO nanoparticles, the cross-linked hybrid hydrogel coating on polyurethane synthetic leather also shows good anti-bacterial capability. 99.99% of Staphylococcus aureus can be killed on the surface. Based on the good ability to remove formaldehyde and to kill bacteria, the obtained microfiber-based polyurethane cross-linked with a hybrid hydrogel coating containing a multi-scale channel structure can be used in a broad field of applications, such as furniture and car interior parts, to simultaneously solve the indoor air pollution and hygiene problems.

Swellable Array Strategy Based on Designed Flexible Double Hypercross-linked Polymers for Synergistic Adsorption of Toluene and Formaldehyde

High-capacity adsorption and removal of complex volatile organic compounds (VOCs) from real-world environments is a tough challenge for researchers. Herein, a swellable array adsorption strategy was proposed to realize the synergistic adsorption of toluene and formaldehyde on the flexible double hypercross-linked polymers (FD-HCPs). FD-HCPs exhibited multiple adsorption sites awarded by a hydrophobic benzene ring/pyrrole ring and a hydrophilic hydroxyl structural unit. The array benzene ring, hydroxyl, and pyrrole N sites in FD-HCPs effectively captured toluene and formaldehyde molecules through π-π conjugation and electrostatic interaction and weakened their mutual competitive adsorption. Interestingly, the strong binding force of toluene molecules to the skeleton deformed the pore structure of FD-HCPs and generated new adsorption microenvironments for the other adsorbate. This behavior significantly improved the adsorption capacity of FD-HCPs for toluene and formaldehyde by 20% under multiple VOCs. Moreover, the pyrrole group in FD-HCPs greatly hindered H₂O molecule diffusion in the pore, thus efficiently weakening the competitive adsorption of H₂O toward VOCs. These fascinating properties enabled FD-HCPs to achieve synergistic adsorption for multicomponent VOC vapor under a highly humid environment and overcame single-species VOC adsorption properties on state-of-the-art porous adsorbents. This work provides the practical feasibility of synergistic adsorption to remove complex VOCs in real-world environments.

Alginate@Fe3O4@Bentonite nanocomposite for formaldehyde removal from synthetic and real effluent: optimization by central composite design

In this study, Alginate@ Fe₃O₄/Bentonite nanocomposite was utilized to eliminate formaldehyde from wastewater. Structural features of bentonite, bentonite@Fe₃O₄, and Alginate@Fe₃O₄@Bentonite were determined using FT-IR, PXRD, Mapping, EDX, TEM, SEM, VSM, and BET analyses. The central composite design method was employed to find the optimal conditions for formaldehyde removal using Alg@Fe₃O₄@Bent nanocomposite. The maximum formaldehyde uptake efficiency (94.56%) was obtained at formaldehyde concentration of 10.69 ppm, the nanocomposite dose of 1.28 g/L, and pH of 9.96 after 16.53 min. Also, Alginate@Fe₃O₄@Bentonite composite was used to eliminate formaldehyde from Razi petrochemical wastewater and was able to eliminate 91.24% of formaldehyde, 70% of COD, and 68.9% of BOD₅. The isotherm and kinetic investigations demonstrated that the formaldehyde uptake process by the foresaid adsorbent follows the Langmuir isotherm and quasi-first-order kinetic models, respectively. Also, the maximum uptake capacity was obtained at 50.25 mg/g. Moreover, the formaldehyde uptake process by the aforementioned nanocomposite was exothermic and spontaneous. Furthermore, the formaldehyde adsorption efficiency decreased slightly after six reuse cycles (less than 10%), indicating that Alginate@Fe₃O₄@Bentonite nanocomposite has remarkable recyclability. Besides, the influence of interfering ions like nitrate, carbonate, chloride, phosphate, and sulfate was studied on the formaldehyde removal efficiency and the results displayed that all ions except nitrate ion have low interaction with formaldehyde (less than 3% reduction in removal efficiency).

Contribution Evaluation of Physical Hole Structure, Hydrogen Bond, and Electrostatic Attraction on Dye Adsorption through Individual Experiments

Disagreements over various unanswered questions about contribution of the adsorption process and functional groups on dye adsorption still exist. The main aim of this research was to evaluate the contributions of physical hole structure, hydrogen bond, and electrostatic attraction on dye adsorption. Three ideal representatives, namely, a sponge with porous structure, P(AM) containing -CONH2 groups, and P(AANa/AM) containing -COONa groups, were chosen to evaluate the above contributions. The methylene blue (MB) removal rates of these three products were compared through individual experiments. The results revealed that physical hole structure did not play a role in decreasing dye concentration. Hydrogen bond existed in dye adsorption but did not remarkably reduce dye concentration. The excellent removal results of P(AANa/AM) demonstrated that electrostatic attraction was critical in enriching dye contaminants from the solution into solid adsorbent. The results could provide insights into the dye adsorption mechanisms for further research.

Conjugated Microporous Poly(aniline) Enabled Hierarchical Porous Carbons for Hg(II) Adsorption

Hierarchical porous carbons equipped with heteroatoms and diffusion pores have a wide application prospect in adsorption. Herein, we report N-autodoped porous carbons (PTPACs), which were derived from rigid N-rich conjugated microporous poly(aniline)s (CMPAs) and show their all-around applicability in heavy metal adsorption. Their molecular structure could be delicately tuned from 3D organic networks to graphitic carbons through simply adjusting the pyrolysis temperature, affording unique hybrid features of hierarchical micro-meso-macroporosity and amount-tunable nitrogen defects, as validated by the enhanced CO₂ adsorption capacities reaching 5.0 mmol g^-1, a 230% increase compared to the precursor (2.15 mmol g^-1). They therefore show promising a Langmuir adsorption capacity of 434.8 mg g^-1 toward mercury ions, which could be rapidly achieved within a short 20 min. Based on the comprehensive experimental, characterization, and DFT calculation studies, we rationally reveal these impressive adsorptions arise from the hybrid function of chemisorption contributed by populated nitrogen defects and physical adsorption achieved by synergistic functions in the diffusion and storage pores. Outcomes mark the high merits of PTPACs in addressing recent global challenges in environmental engineering.

UV-vis spectroscopic detection of formaldehyde and its analogs: A convenient and sensitive methodology

Formaldehyde is deemed to be an indispensable industrial product that has been widely applied in manufacture of resins, drugs, building materials, etc. It has been widely accepted that, nevertheless, residual formaldehyde will cause pathogen reactions, even leading to cancers like leukemia. Thus, a facile and efficient approach has been designed to achieve the determination of formaldehyde by ultraviolet and visible (UV-vis) spectrophotometry in liquid media. In detail, O-(carboxymethyl) hydroxylamine (C₂H₅NO₃·0.5HCl) is chosen as the detection reagent for the specific recognition of formaldehyde on account of its unique aminooxy (-O-NH₂) which can react with formaldehyde to form oxime bonds (O-NCH₂), accompanied with the only by-product of H₂O. Likewise, this simple and sensitive detection approach based on the chemical detection reagent C₂H₅NO₃·0.5HCl can also be applied to the determination of other aldehyde homologs with carbonyl groups including acetaldehyde, acetone, benzaldehyde, 1, 4-phthalaldehyde. As a result, all the UV absorbances of analytes display remarkable linear detection relationships. The limits of detection (LOD) and limits of quantitation (LOQ) values are in the range of 0.03-1.16 ppm and 0.03-5.81 ppm respectively, with RSDs of 3.27-3.75 %, evidencing the feasibility of our method to determine formaldehyde and its homologs by UV-vis spectrophotometry and auspicious prospects of practical applications.

An electroactive montmorillonite/polypyrrole ion exchange film: Ultrahigh uptake capacity and ion selectivity for rapid removal of lead ions

Contact with trace heavy metal contaminants will also lead to extremely bad health influence on human body and aquatic life. Although various adsorbents have been synthesized for the recovery of heavy metal ions, most of them shows deficient adsorption capacity, sluggish uptake rate and low selectivity. In this study, a montmorillonite/polypyrrole (MMT/PPy) film was successfully synthesized by intercalating polymers PPy into the interlayer of MMT nanosheets for selective and rapid capture of Pb²⁺. The electroactive film has ultrahigh uptake capacity (1373.29 mg⋅g^-1), which is much higher than most conventional Pb²⁺ adsorbents. Meanwhile, it had an extreme selectivity towards Pb²⁺ due to the MMT/PPy film can accurately identified Pb²⁺. Through characterization testing and data analysis, the selective and rapid uptake/release of Pb²⁺ should be realized through three ways: (1) negatively-charged laminates of MMT can generate electrostatic attraction to Pb²⁺; (2) -OH on the surface of MMT laminates can accurately identified and bonded with Pb²⁺ (M-O-H↔ M-O-Pb); (3) PPy doped by PSS^n- and protic acid can rapidly catch Pb²⁺ (PPy⁺·PSS^n-+Pb²⁺+e^-→ PPy·PSS^n-·Pb²⁺). Therefore, such a novel MMT/PPy nanocomposite film could has evident application prospect to remove Pb²⁺ from various water bodies.

Porosity Design on Conjugated Microporous Poly(Aniline)S for Exceptional Mercury(II) Removal

The use of conjugated microporous polymers (CMPs) in practical wastewater treatment demands further design on the pore structure, otherwise their adsorption capacities toward heavy-metal ions were moderate. Here, we report a rational design approach, which produces hybrid molecular pores in conjugated microporous poly(aniline)s (CMPAs) for mercury removal. It is achieved through a delicate interval introduction of linkers with differential molecular lengths during polymerization, acquiring both diffusion channels and storage pores for radical enhancement of mass transfer and adsorption storage. The resulting CMPA-M featured a large adsorption capacity of 975 mg g^-1 and rapid kinetics that could remove 94.8% of 50 mg g^-1 of mercury(II) within a very short contact time of 48 s, with a promising initial adsorption rate h as high as 113 mg g^-1 min^-1, which was 2.54-fold larger in the adsorption capacity and 45.2-fold faster in the adsorption efficiency compared with the undeveloped CMPAs. More importantly, our CMPA-M-2, with robust stability and easy reusability, was able to scavenge over 99.9% of mercury(II) from the actual wastewater in a harsh condition with a very low pH of 0.77, extremely high salinity of 53,157 mg L^-1, and complex impurities, featuring exceptional selectivity that allows us to extract and recycle a high purity of 99.1% of mercury from the wastewater. These outcomes demonstrate the unprecedented potential of CMPs for environmental remediation and real-world mercury extraction and present benchmarks for CMP-based mercury adsorbents.