Facile one-step hydrothermal synthesis of α-Fe2O3/g-C3N4 composites for the synergistic adsorption and photodegradation of dyes

Purification of aqueous orange II solution through adsorption and visible-light-induced photodegradation using ZnO-modified g-C3N4 composites

Semiconductor-based remediation enables environmentally friendly methods of removing aqueous pollutants. Simply fabricated ZnO modified g-C3N4 composites were utilized as bifunctional adsorptive photocatalysts for orange II removal from aqueous solution through adsorption and photocatalysis processes. The adsorption isotherm data of the g-C3N4 (g-CN) and ZnO modified g-C3N4 (ZCN) composites on orange II solution were better fitted with the Langmuir isotherm compared to the Freundlich isotherm. The maximum adsorption capacity for ZCN-2.5 was slightly higher than that of bare g-CN. According to the adsorption thermodynamics investigation of ZCN-2.5 in orange II solution, the positive values of Gibb's free energy change (ΔG0) suggested a non-spontaneous adsorption process. Furthermore, the negative values of entropy change (ΔS) and enthalpy change (ΔH) indicated the decrement of randomness and exothermic nature during the adsorption process, respectively. The photocatalytic degradation kinetics of g-CN and ZCN composites indicated that the degradation process follows the pseudo-first-order reaction kinetic. The degradation rate of orange II with the ZCN-2.5 composite was 6.67 times higher than that obtained with bare g-CN. Possible adsorption and photocatalytic mechanisms have been proposed.

Dependency of Crystal Violet Dye Removal Behaviors onto Mesoporous V2O5-g-C3N4 Constructed by Simplistic Ultrasonic Method

This research examined the production of a V2O5-g-C3N4 nanocomposite to remove organic dyes from wastewater. To generate the V2O5-g-C3N4 nanocomposite, the sonication method was applied. The testing of V2O5-g-C3N4 with various dyes (basic fuchsin (BF), malachite green (MG), crystal violet (CV), Congo red (CR), and methyl orange (MO)) revealed that the nanocomposite has a high adsorption ability towards BF, MG, CV, and CR dyes in comparison with MO dye. It was established that the modification of pH influenced the removal of CV by the V2O5-g-C3N4 nanocomposite and that under optimal operating conditions, efficiency of 664.65 mg g−1 could be attained. The best models for CV adsorption onto the V2O5-g-C3N4 nanocomposite were found to be those based on pseudo-second-order adsorption kinetics and the Langmuir isotherm. According to the FTIR analysis results, the CV adsorption mechanism was connected to π–π interactions and the hydrogen bond.

Ultrathin porous carbon nanosheet as an efficient adsorbent for the removal of bisphenol A: The overlooked role of topological defects

Carbon-based materials are emerging as a type of inexpensive and efficient adsorbent, although their genuine adsorption site is still debatable. Herein, we present a novel approach for designing and constructing an ultra-thin defect-rich hierarchically porous carbon nanosheet (ZG-C). The ZG-C sample demonstrated a high adsorption capacity for bisphenol A (BPA) (602.2 mg/g) along with a fast adsorption process (20 min), and stable reusability (the decline efficiency was 9.14% after five consecutive cycles). Based on comprehensive experiments and a number of characterizations, the high adsorption capacity of ZG-C for BPA was connected with the hierarchical porous structure of ZG-C and multiple intrinsic defects of ZG-C. The results of density functional theory (DFT) further demonstrated that topological defects played an indispensable role in promoting adsorption, and its adsorption energy (-0.595 eV) for BPA was much higher than that of other intrinsic defects. This study not only provides an innovative and simple strategy for preparing hierarchically porous carbon-based adsorbent with abundant intrinsic defects for the efficient removal of BPA, but also significantly contributes to the understanding of the application of carbon-based materials to remove bisphenols.

Effective Removal of Methylene Blue on EuVO4/g-C3N4 Mesoporous Nanosheets via Coupling Adsorption and Photocatalysis

In this study, we first manufactured ultrathin g-C₃N₄ (CN) nanosheets by thermal etching and ultrasonic techniques. Then, EuVO₄ (EV) nanoparticles were loaded onto CN nanosheets to form EuVO₄/g-C₃N₄ heterojunctions (EVCs). The ultrathin and porous structure of the EVCs increased the specific surface area and reaction active sites. The formation of the heterostructure extended visible light absorption and accelerated the separation of charge carriers. These two factors were advantageous to promote the synergistic effect of adsorption and photocatalysis, and ultimately enhanced the adsorption capability and photocatalytic removal efficiency of methylene blue (MB). EVC-2 (2 wt% of EV) exhibited the highest adsorption and photocatalytic performance. Almost 100% of MB was eliminated via the adsorption–photocatalysis synergistic process over EVC-2. The MB adsorption capability of EVC-2 was 6.2 times that of CN, and the zero-orderreaction rate constant was 5 times that of CN. The MB adsorption on EVC-2 followed the pseudo second-order kinetics model and the adsorption isotherm data complied with the Langmuir isotherm model. The photocatalytic degradation data of MB on EVC-2 obeyed the zero-order kinetics equation in 0–10 min and abided by the first-order kinetics equation for10–30 min. This study provided a promising EVC heterojunctions with superior synergetic effect of adsorption and photocatalysis for the potential application in wastewater treatment.

Lignite-Based N-Doped Porous Carbon as an Efficient Adsorbent for Phenol Adsorption

The treatment of phenolic-containing wastewater has received increased attention in recent years. In this study, the N-doped porous carbons were prepared from lignite with tripolycyanamide as the N source, and their phenol adsorption behaviors were investigated. Results clearly showed that the addition of tripolycyanamide largely improved the surface area, micropore volume, N content and thus the phenol adsorption capacity of lignite-based carbons. The N-doped sample prepared at 700 °C showed a surface area of 1630 m2/g and a phenol adsorption capacity as high as 182.4 mg/g at 20 °C, which were 2.0 and 1.6 times that of the lignite-based carbon without N-doping. Pseudo-second order and Freundlich adsorption isotherm models could better explain the phenol adsorption behaviors over lignite-based N-doped porous carbon. Theoretical calculations demonstrated that phenol adsorption energies over graphitic-N (−72 kJ/mol) and pyrrolic-N (−74 kJ/mol) groups were slightly lower than that over the N-free graphite layer (−71 kJ/mol), supporting that these N-containing groups contribute to enhance the phenol adsorption capacity. The adsorption mechanism of phenol over porous carbon might be interpreted by the π–π dispersion interactions between aromatic-ring and carbon planes, which could be enhanced by N-doping through increasing π electron densities in the carbon plane.

Ring defects-rich and pyridinic N-doped graphene aerogel as floating adsorbent for efficient removal of tetracycline: Evidence from NEXAFS measurements and theoretical calculations

The rational design of carbon-based adsorbents with a high uptake efficiency for polar organic molecules is a key challenge in water purification research. Herein, we report a graphene aerogel that is doped with pyridinic-N and has abundant ring defects (denoted by DNGA). The aerogel sample exhibits a high adsorption capacity of 607.1 mg/g toward tetracycline (TC), a fast adsorption process (20 min), and good reusability (with a declining efficiency < 10.0% after five cycles), while being easy to recycle. C/N K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that the efficient adsorption capacity of the DNGA sample is related to the presence of ring defects and the pyridinic-N species. Density functional theory (DFT) calculations demonstrate that ring defects of type 5-8-5 and the pyridinic-N species at the edge location are primarily responsible for TC removal. In this study, we resolve a controversial issue regarding the origin of the adsorption performance origin of N-doped carbon-based adsorbents. The findings of this study can guide the development of novel and improved N-doped carbon-based adsorbents for the removal of target contaminants.

A 2D/1D heterojunction nanocomposite built from polymeric carbon nitride and MIL-88A(Fe) derived α-Fe2O3 for enhanced photocatalytic degradation of rhodamine B

2D/1D heterojunction α-Fe2O3/C3N4 photocatalysts containing α-Fe2O3 microrods and polymeric carbon nitride flakes are synthesised through the calcination of Fe-based metal-organic frameworks and boost the visible light photocatalytic degradation of rhodamine B.

Mechanistic understanding of highly selective adsorption of bisphenols on microporous-dominated nitrogen-doped framework carbon

Producing a desirable adsorbent for removing endocrine disrupting compounds (EDCs) from aqueous solutions remains a major challenge. In this work, microporous-dominated nitrogen-doped framework carbons (MNFCs, s means the calcination temperature) with high specific surface area, ultra-microporous structure, and high nitrogen-doping can be obtained by a direct calcination of ethylene diamine tetraacetic acid tetrasodium (EDTA-4Na) without aid of any catalyst and nitrogen source. MNFCs were applied adsorbents to remove bisphenols from aqueous solution. Batch experiments showed MNFC-750 had a large adsorption capacity for bisphenols from aqueous solutions (409 mg/g for bisphenol A, 364 mg/g for bisphenol F, and 521 mg/g for bisphenol S) along with short equilibrium time (30 min), and good stability and reusability. Using multiple characterizations and comparative experiments along with theoretical calculations, we discovered that: (1) nitrogen-doping can significantly boost the adsorption capacity; (2) adsorption sites are mainly the pyridinic-N instead of pyrrolic-N and graphitic-N; and (3) the adsorption mechanisms were mainly driven by Lewis acid-base interaction, hydrophobic interaction, π-π interaction and hydrogen bond interaction. These findings indicate that MNFCs present a promising potential for practical applications and shed light on the rational design of nitrogen doped carbon-based adsorbents for efficient pollutant removal.

Fabrication, application, optimization and working mechanism of Fe2O3 and its composites for contaminants elimination from wastewater

Fe₂O₃ and its composites have been extensively investigated and employed for the remediation of contaminated water with the characteristics of low cost, outstanding chemical stability, high efficiency of visible light utilization, excellent magnetic ability and abundant active sites for adsorption and degradation. In this review, the potentials of Fe₂O₃ in water remediation were discussed and summarized in detail. Firstly, various synthesis methods of Fe₂O₃ and its composites were reviewed and compared. Based on the structures and characteristics of the obtained materials, their applications and related mechanisms in pollutants removal were surveyed and discussed. Furthermore, several strategies for optimizing the remediation processes, including dispersion, immobilization, nano/micromotor construction and simultaneous decontamination, were also highlighted and discussed. Finally, recommendations for further work in the development of novel Fe₂O₃-related materials and its practical applications were proposed.

A novel ternary magnetic Fe3O4/g-C3N4/Carbon layer composite for efficient removal of Cr (VI): A combined approach using both batch experiments and theoretical calculation

Heavy metal pollution has posed a potential hazard to the ecological environment and human health. Herein, a novel ternary magnetic adsorbent (Fe₃O₄/g-C₃N₄/Carbon layer, Carbon layer: hydrothermal products from sucrose) was synthesized through a simple hydrothermal carbonization (HTC) method for removal of hexavalent chromium (Cr (VI)) removal. The Carbon layer (CL) formed during the HTC of carbon precursors (sucrose) acted as a reducing agent. Also, it has abundant oxygen-containing groups on its surface. The Fe₃O₄/g-C₃N₄/CL had a high removal capacity for Cr (VI) (50.09 mg/g), and excellent regeneration and magnetic separation performance. Importantly, the Fe₃O₄/g-C₃N₄/CL could not only improve the adsorption ability for Cr (VI), but also strengthen the immobilization of Cr (III). Based on the comprehensive experiments and characterization, combined with DFT calculations, we proposed that, the first time, the removal of Cr (VI) was controlled by three consecutive processes: (1) ion exchange of Cr (VI) by hydroxyl groups, (2) reduction of Cr (VI) to Cr (III) by electron-donor (oxygen-containing) groups (EDGs), and (3) complexation of Cr (III) by amine groups. This study provides a new avenue for the removal of toxic oxygen anions and reveals an original removal mechanism of Fe₃O₄/g-C₃N₄/CLx (x = hydrothermal products from carbon precursors (glucose, ascorbic acid, cellulose)).

Superior Adsorption and Photocatalytic Degradation Capability of Mesoporous LaFeO3/g-C3N4 for Removal of Oxytetracycline

Mesoporous LaFeO3/g-C3N4 Z-scheme heterojunctions (LFC) were synthesized via the incorporation of LaFeO3 nanoparticles and porous g-C3N4 ultrathin nanosheets. The as prepared LFC were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, Raman spectra and N2 adsorption analysis. The structural analysis indicated that the reheating process and the addition of NH4Cl in the thermal polymerization were the key factors to get porous g-C3N4 ultrathin nanosheets and to obtain high specific surface areas of LFC. It remarkably enhanced the adsorption capacity and photocatalytic degradation of LFC for removal of oxytetracycline (OTC). The effect of the mass percentage of LaFeO3 in LFC, pH and temperature on the OTC adsorption was investigated. The LaFeO3/g-C3N4 heterojunction with 2 wt % LaFeO3 (2-LFC) exhibited highest saturated adsorption capacity (101.67 mg g−1) and largest photocatalytic degradation rate constant (1.35 L g−1 min−1), which was about 9 and 5 times higher than that of bulk g-C3N4 (CN), respectively. This work provided a facile method to prepare mesoporous LaFeO3/g-C3N4 heterojunctions with especially well adsorption and photocatalytic activities for OTC, which can facilitate its practical applications in pollution control.