Triazine-Based Functionalized Activated Carbon Prepared from Water Hyacinth for the Removal of Hg2+, Pb2+, and Cd2+ Ions from Water

Detection and mapping of the seasonal distribution of water hyacinth (Eichhornia crassipes) and valorization as a biosorbent of Pb(II) in water

In the present research, the presence of water hyacinth (Eichhornia crassipes) on the surface of the San Jose Dam located in the city of San Luis Potosi, S.L.P, Mexico, was monitored and mapped. The monitoring was conducted for 2 years (2018-2020) with remote sensing data from OLI Landsat 8 sensors, based on the normalized difference vegetation index (NDVI). The results demonstrated the capability and accuracy of this method, where it was observed that the aboveground cover area, proliferation, and distribution of water hyacinth are influenced by climatic and anthropogenic factors during the four seasons of the year. As part of a sustainable environmental control of this invasive species, the use of water hyacinth (WH) root (RO), stem (ST), and leaf (LE) components as adsorbent material for Pb(II) present in aqueous solution was proposed. The maximum adsorption capacity was observed at pH 5 and 25 °C and was 107.3, 136.8, and 120.8 mg g-1 for RO, ST, and LE, respectively. The physicochemical characterization of WH consisted of scanning electron microscopy (SEM), N2 physisorption, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), charge distribution, and zero charge point (pHPZC). Due to the chemical nature of WH, several Pb(II) adsorption mechanisms were proposed such as electrostatic attractions, ion exchange, microprecipitation, and π-cation.

Hydrothermal synthesis of Mg/Al-layered double hydroxide modified water hyacinth hydrochar for remediation of wastewater containing mordant brown dye

A high-performance dye adsorbent of Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH) was synthesized by a simple hydrothermal method. The surface functional groups, elemental composition, crystalline structure, and surface morphology of the prepared (MgAl@WH) were determined using different analytical techniques. The characterization results revealed that the (MgAl@WH) hydrochar surface offered more active adsorption sites, facilitating the mordant brown (anionic dye) adsorption, leading to its superior performance with much higher uptake capability (311.0 mg g-1 at 298 K) than Mg/Al double hydroxide nanosheets (MgAl DLHs, 80.2 mg g-1 at 298 K) and dried water hyacinth (WH, 10.0 mg g-1 at 298 K). The adsorption behavior of MgAL@WH follows the pseudo second order kinetic model (R2 = 0.999) and Langmuir isotherm model (R2 = 0.999). Moreover, MgAl@WH bonded efficiently with mordant brown dye via hydrogen bonding and interlayer anion exchange with monolayer formation. Additionally, the recycling tests revealed that the MgAl@WH can be reused over 10 cycles without significant change in the removal efficiency. Based on the obtained findings, Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH), for its economic and environmental benefits, has recently been used as an efficient adsorbent to remediate industrial wastewater containing anionic dyes.

Supramolecular Modular Assembly of Imaging-Trackable Enzymatic Nanomotors

Self-propelled micro/nanomotors (MNMs) have shown great application potential in biomedicine, sensing, environmental remediation, etc. In the past decade, various strategies or technologies have been used to prepare and functionalize MNMs. However, the current preparation strategies of the MNMs were mainly following the pre-designed methods based on specific tasks to introduce expected functional parts on the various micro/nanocarriers, which lacks a universal platform and common features, making it difficult to apply to different application scenarios. Here, we have developed a modular assembly strategy based on host-guest chemistry, which enables the on-demand construction of imaging-trackable nanomotors mounted with suitable driving and imaging modules using a universal assembly platform, according to different application scenarios. These assembled nanomotors exhibited enhanced diffusion behavior driven by enzymatic reactions. The loaded imaging functions were used to dynamically trace the swarm motion behavior of assembled nanomotors with corresponding fuel conditions both in vitro and in vivo. The modular assembly strategy endowed with host-guest interaction provides a universal approach to producing multifunctional MNMs in a facile and controllable manner, which paves the way for the future development of MNMs systems with programmable functions.

Enhanced adsorption of Pb2+ by the oxygen-containing functional groups enriched activated carbon

Lead is one of the primary pollutants found in water and poses significant toxicity risks to humans; thus, it is necessary to investigate techniques for removing it economically and efficiently. In order to enhance the removal capacity of Pb2+, coconut shell-based activated carbon (AC) was modified with introducing oxygen-containing functional groups (OFGs) via nitric acid (HNO3) or hydrogen peroxide (H2O2) modification in this study. The characterization results show that after oxidation treatment, the content of OFGs increased, and the textural properties of the samples do not change significantly. This indicates that the modification conditions used in this study effectively introduced OFGs while avoiding the adverse effects on physical adsorption ability of AC caused by oxidation treatment. The Pb2+ adsorption capacities of the AC modified with 10 M HNO3 and 30 wt.% H2O2 were 4.26 and 3.64 times that of the pristine AC, respectively. The experimental data can be well fitted using the Langmuir isotherm model and the Elovich kinetic model, suggesting that the adsorption of Pb2+ on AC belongs to single-layer adsorption, and chemical adsorption dominates the adsorption process. In summary, the hydrothermal-assisted HNO3/H2O2-modified coconut shell-based AC shows great potential in efficiently removing Pb2+ from solutions, offering a solution for utilizing coconut shell waste.

The key role of unsaturated olefin content on polysulfides prepared via inverse vulcanization of waste plant oils for mercury removal from wastewater

Three waste plant oils (olive oil, coconut oil, and soybean oil) were utilized as monomer crosslinking agents to synthesize polysulfides by inverse vulcanization with elemental sulfur, for mercury removal from wastewater. NMR analysis showed that 92.1% of the olefins participated in the inverse vulcanization reaction, indicating that the quantity of unsaturated olefins in plant oil mainly affects the ring-opening ratio of sulfur for the formation of sulfur-based polymers. The experimental results showed that olive oil polysulfide (S-r-olive) achieved 100% Hg2+ removal within 2 h at a pH of 6. The S-r-olive, S-r-soybean, and S-r-coconut exhibited adsorption capacities of 130.23, 42.72, and 28.08 mg/g, respectively. The kinetic and adsorption isotherm illustrated that the Hg2+ adsorption by polysulfides conformed to the pseudo-second-order and Freundlich models, showing that the reaction rate constant of S-r-olive is approximately 14 times and 4.6 times greater than that of S-r-soybean and S-r-coconut, respectively. The adsorption mechanism is concluded that Hg2+ first enters the suspended S-r-olive by physical adsorption, then combined with sulfur to form HgS by chemical action and fixed in the S-r-olive adsorbent. This study demonstrates that utilizing waste plant oils as monomer crosslinking agents to synthesize adsorbents for Hg2+ removal is feasible and effective.

Removal of Cr6+ ions and mordant violet 40 dye from liquid media using Pterocladia capillacea red algae derived activated carbon-iron oxides

In recent years, water pollution has become one of the most dangerous problems facing the world. Pollution of water with heavy metals and different dyes has caused many harmful effects on human health, living organisms and our environment. In this study, iron oxide nanomagnetic composite from Pterocladia Capillacea red algae-derived activated carbon (PCAC-IO) was synthesized by co-precipitation method using different iron salts and different base solutions. The synthesized nanocomposite was investigated with various characterization techniques such as FTIR, BET, SEM-EDX, TEM, XRD, and VSM. The obtained PCAC-IO adsorbent was used for Cr6+ ions and Mordant Violet 40 (MV40) dye removal. The adsorption mechanism of Cr6+ ions and MV40 dye on PCAC-IO was examined using several adsorption and kinetic isotherm models. Langmuir and Freundlich models were investigated using experimental data. Pseudo-first-order (PFO), Pseudo-second-order (PSO) and intraparticle diffusion models (IPDM) were applied to identify the adsorption mechanism. It has shown that the PSO kinetic model fits better with the experimental data obtained from PCAC-IO. This result can be interpreted as the adsorption of the adsorbate on the nanocomposite as chemical adsorption. The optimum conditions for maximum Cr6+ ions removal (96.88%) with PCAC-IO adsorbent occur at room temperature, 5 g L-1 adsorbent concentration, 100 mg L-1 initial pollutant concentration, pH 1 and at the end of 180 min, while maximum MV40 dye removal (99.76%), other conditions being the same, unlikely it occurred at pH 2.06 and after 45 min. The most suitable model for Cr6+ ions removal under the conditions of 1 L-1 g adsorbent concentration and 400 mg L-1 adsorbate concentration was Langmuir (Qmax = 151.52 mg g-1), while for MV40 removal it was Freundlich (Qmax = 303.03 mg g-1). We propose the use of activated carbon-supported iron oxide prepared from bio-waste material, especially from Pterocladia Capillacea red algae, as a promising adsorbent with high efficiency in the removal of Cr6+ ions and MV40 dye from aqueous media.

Electrochemical sensor based on amine- and thiol-modified multi-walled carbon nanotubes for sensitive and selective determination of uranyl ions in real water samples

Novel selective and sensitive electrochemical sensors based on the modification of a carbon paste electrode (CPE) with novel amine- and thiol-functionalized multi-walled carbon nanotubes (MWCNT) have been developed for the detection and monitoring of uranyl ions in different real water samples. Multiwalled carbon nanotubes were grafted with 2-aminothiazole (AT/MWCNT) and melamine thiourea (MT/MWCNT) via an amidation reaction in the presence of dicyclohexyl carbodiimide (DCC) as a coupling agent. This modification for multiwalled carbon nanotubes has never been reported before. The amine and thiol groups were considered to be promising functional groups due to their high affinity toward coordination with uranyl ions. The modified multi-walled carbon nanotubes were characterized using different analytical techniques including FTIR, SEM, XPS, and elemental analysis. Subsequently, 10 wt% MT/MWCNT was mixed with 60 wt% graphite powder in the presence of 30 wt% paraffin oil to obtain a modified carbon paste electrode (MT/MWCNT/CPE). The electrochemical behavior and applications of the prepared sensors were examined using cyclic voltammetry, differential pulse anodic stripping voltammetry, and electrochemical impedance spectroscopy. The MT/MWCNT/CPE sensor exhibited a good linearity for UO22+ in the concentration range of 5.0 × 10-3 to 1.0 × 10-10 mol L-1 with low limits of detection (LOD = 2.1 × 10-11 mol L-1) and quantification (LOQ = 7 × 10-11 mol L-1). In addition, high precision (RSD = 2.7%), good reproducibility (RSD = 2.1%), and high stability (six weeks) were displayed. Finally, MT-MWCNT@CPE was successfully utilized to measure the uranyl ions in an actual water sample with excellent recoveries (97.8-99.3%). These results demonstrate that MT-MWCNT@CPE possesses appropriate accuracy and is appropriate for environmental applications.

Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

Isotherm and kinetic studies of acid yellow 11 dye adsorption from wastewater using Pisum Sativum peels microporous activated carbon

In this study, Pea Peels-Activated Carbon (PPAC), a novel biochar, was created from leftover pea peels (Pisum sativum) by wet impregnation with ZnCl₂ and subsequent heating to 600, 700, and 800 °C in a CO₂ atmosphere. Investigated how the newly acquired biochar affected the capacity to extract the AY11 dye from the aqueous solution. Through the use of FTIR, XRD, SEM, BJH, BET, DSC, EDX, and TGA studies, the prepared PPAC was identified. It was found that a pH of 2 is optimum for the AY11 dye elimination. The highest removal percentage of AY11 dye was 99.10% using a beginning AY11 dye concentration of 100 mg/L and a 1.0 g/L dose of PPAC. The highest adsorption capacity (Q_m) of the PPAC was 515.46 mg/g. Freundlich (FIM), Halsey (HIM), Langmuir (LIM), Tempkin (TIM), and Gineralize (GIM) isotherm models were useful in examining the adsorption results. A variety of error functions, including the average percent errors (APE), root mean square errors (RMS), Marquardt's percent standard deviation (MPSD), hybrid error function (HYBRID), Chi-square error (X²) and a sum of absolute errors (EABS) equations, were also applied to test the isotherm models data. The PPAC experimental data were best suited by the HIM and FIM isotherm models. Elovich (EM), Pseudo-first-order (PFOM), Intraparticle diffusion (IPDM), Pseudo-second-order (PSOM), and Film diffusion (FDM) models were applied to study the kinetic adsorption results. The PSOM had a strong correlation coefficient (R² > 0.99), and it was principally responsible for controlling the adsorption rate. Anions are typically absorbed during the adsorption mechanism of AY11 dye by PPAC owing to attractive electrostatic forces created with an increase in positively charged areas at acidic pH levels. The regenerated PPAC was used in six successive adsorption/desorption cycles. This study's outcomes show that PPAC successfully removes the AY11 dye from the aqueous solution; as a result, PPAC can be used repeatedly without experiencing considerable loss in effectiveness.

Highly fluorescent hydroxyl groups functionalized graphitic carbon nitride for ultrasensitive and selective determination of mercury ions in water and fish samples

Heavy metal ion pollution is always a serious problem worldwide. Therefore, monitoring heavy metal ions in environmental water is a crucial and difficult step to ensure the safety of people and the environment. A mercury ion (Hg2+) fluorescence probe with excellent sensitivity and selectivity is described here. The functionalized graphitic carbon nitride nanosheets (T/G-C3N4) fluorescence probe was fabricated using melamine as a precursor by the pyrolysis technique, followed by a rapid KOH heat treatment method for 2 min. The chemical structure and morphology of the T/G-C3N4 probe were characterized using multiple analytical techniques including UV–Vis, SEM, XPS, XRD, and fluorometer spectroscopy. Geometry optimization of T/G-C3N4 as a modified probe was performed to assess its stability and interaction ability with Hg(II) via using the density function approach. The T/G-C3N4 probe showed a linear response based on quenching over the range 0–1.25 × 103 nM Hg(II); the detection limit was 27 nM. The remarkable sensitivity of T/G-C3N4 towards the Hg2+ ions was explained by the intense coordination and fast chelation kinetics of Hg2+ with the NH2, CN, C=N, and OH groups of T/G-C3N4 nanoprobe. The T/G-C3N4 probe demonstrates exceptional selectivity for Hg2+ ions among other metal ions including (Na+, Ag+, Mg2+, Fe2+, Fe3+, Co2+, Ni2+, Cd2+, K+, Ca2+, Cu2+, Pb2+, Mn2+ and Hg2+) and over a broad pH range (6–10), together with remarkable long-term fluorescence stability in water (> 30 days) and minimal toxicity. T/G-C3N4 was used to detect and quantify Hg2+ ions in tuna and mackerel fish and the results compared to ICP-AES. The results obtained offer a new simple and green technique for the design of multifunctional fluorescent probe appropriate for environmental applications.

Graphical Abstract

Enhanced performance of hydroxyl and cyano group functionalized graphitic carbon nitride for efficient removal of crystal violet and methylene blue from wastewater

This work reports the synthesis of an innovative multifunctional carbon nitride based adsorbent and its successful application for the removal of crystal violet (CV) and methylene blue (MB) from wastewater. The functionalized graphitic carbon nitride (f/g-CN) adsorbent was produced by the pyrolysis of melamine followed by thermal alkali treatment to introduce OH, NH x , and CN groups onto the graphitic carbon nitride (g-CN) surface. Experimental data obtained from batch tests revealed that the maximum adsorption capacities of g-CN and f/g-CN were found to be 28.9 and 239.0 mg g-1 for MB, and 163.0 and 532.0 mg g-1 for CV, respectively, at pH 8, 25 °C and after 90 min. This increase in adsorption capacity of f/g-CN can be explained by the presence of multiple functional groups in its structure. f/g-CN showed 100% removal for MB and CV with concentrations lower than 100 ppm and the equilibrium time required for the 100% removal of 500 ppb dye is 60 seconds. Additionally, the experimental data fitted well with the Langmuir isotherm model (R 2 = 0.992) and pseudo second order kinetic model (R 2 = 0.999) suggesting that the mechanism of adsorption is based on π-π stacking and electrostatic interactions between the NH x and OH groups of f/g-CN and dye molecules with monolayer formation. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 7 cycles. This work highlights the merits of the prepared adsorbent f/g-CN which is an eco-friendly, stable, efficient, and reusable adsorbent for removing cationic dyes from wastewater.