Turning date palm waste into carbon nanodots and nano zerovalent iron composites for excellent removal of methylthioninium chloride from water

Production of activated carbon from date palm stones by hydrothermal carbonization and microwave assisted KOH/NaOH mixture activation for dye adsorption

Date palm stones are regarded as possible alternatives to activated carbon (AC) precursors with high potential for various environmental applications. In this research study, date palm stones derived activated carbon (DPSAC) was used as adsorbent for removing toxic remazol brilliant blue R (RBBR). The synthesis of DPSAC involved a chemical treatment using KOH and NaOH (1:1). Characterization of DPSAC revealed that it exhibited a BET surface area of 715.30 m2/g, Langmuir surface area of 1061.93 m2/g, total pore volume of 0.39 cm3/g, and average pore diameter of 2.15 nm. Adsorption uptake of RBBR increased (from 24.54 to 248.54 mg/g), whereas the removal percentage decreased (from 98.16 to 82.85%) when the initial RBBR concentration increased (from 25 to 300 mg/L). The adsorption process performed best under acidic conditions (pH 3), with an RBBR uptake of 98.33 mg/g. Because of the high R2 values (0.9906 and 0.9779) and low average errors (6.24 and 13.95%), this adsorption process followed the Freundlich isotherm and pseudo-first-order (PFO) models, respectively. The Langmuir adsorption capacity (Qm) was 319.63 mg/g. Thermodynamic parameters were - 11.34 kJ/mol for ∆H° (exothermic in nature), 0.05 kJ/mol K for ∆S° (increasing randomness level at solid-liquid interface), - 27.37 kJ/mol for ∆G° (spontaneous), and 6.84 kJ/mol for Ea (controlled by physisorption).

Removal of water pollutants using plant-based nanoscale zero-valent iron: A review

Nanotechnology has been increasingly explored for the treatment of various waste streams. Among different nanoparticles, nanoscale zerovalent iron (nZVI) has been extensively investigated due to its high reactivity and strong reducing power. However, conventional methods for the synthesis of nZVI particles have several limitations and led to the green synthesis of nZVI using plant-based materials. Plant extracts contain various reducing agents that can be used for nZVI synthesis, eliminating the need for toxic chemicals, and reducing energy consumption. Additionally, each plant species used for nZVI synthesis results in unique physicochemical properties of the nanoparticles. This review paper provides an overview of plant-based nZVI particle synthesis, its characteristics, and its application for the removal of different classes of pollutants such as dyes, heavy metals, nutrients, and trace organic pollutants from water. The review shows that continued research on plant-based nZVI particles to fully understand its potential in wastewater treatment, especially for the removal of a wider variety of pollutants, and for improving sustainability and reducing the cost and environmental impact of the process, is necessary.

Fluorescent carbon dots from water hyacinth as detection sensors for ferric ions: the preparation and optimisation using response surface methodology

The search for alternatives to chemicals from natural products as precursors for the preparation of highly doped carbon dots (CDs) remains challenging. Novel CDs (W-CDs) were synthesised using a one-step pyrolysis method with wastewater hyacinth as the sole carbon and nitrogen source at a mild temperature without using any surface-activating reagents or salt. The obtained W-CDs emitted strong blue fluorescence under 365 nm UV light excitation, with a quantum yield of 15.12%. The Box-Behnken design of the response surface methodology was applied to optimize the W-CD preparation conditions, including the reaction temperature, reaction time and weight of water hyacinths. The temperature was found to be the most important factor affecting the fluorescence intensity of the W-CDs. Additionally, the fluorescence sensor based on W-CDs demonstrated excellent selectivity towards ferric (Fe) ions, with a limit of detection of 2.35 μM. The fluorescent sensor was successfully applied for detecting Fe³⁺ in real water samples with a recovery of 97.80-103.10%. Hence, the pyrolysis of water hyacinth is proven to be a rapid, effective and green approach for CDs and provides a novel method for recycling water hyacinth.

Spatial–Temporal Variations of Water Ecosystem Services Value and Its Influencing Factors: A Case in Typical Regions of the Central Loess Plateau

Water resources provide indispensable ecosystem services, which are related to human well-being and sustainable social development. Accurately measuring the water ecosystem services value (WESV), and then grasping its changing characteristics, is particularly important for solving water problems. In this study, the typical area of the central Loess Plateau location is taken as the research area. Based on remote sensing images and statistical data, the direct market method combined with the equivalent factor method was used to calculate the WESV including groundwater and surface water, which is of greatest originality. The temporal and spatial variation characteristics in 2010, 2015 and 2020 were analyzed. Then, four WESV driving factors including per capita GDP, population density, proportion of water areas, and water consumption were selected, and the geographically weighted regression (GWR) model was used to analyze the spatial distribution pattern and temporal variation of WESV’s response to the influencing factors. The results showed that WESV experienced a process of first decreasing and then increasing, which was mainly caused by Yulin. For the composition of WESV, the proportion of provisioning services value has increased, which caused the proportion of regulating services value to decrease. The correlations between four factors and WESV were different. The distribution pattern of the influences was spatially heterogeneous, which showed regular variations over time. These results indicate the necessity of WESV’s independent research and provide a realistic basis for ecological compensation in the Yellow River Basin.

Comprehensive review on synthesis, physicochemical properties, and application of activated carbon from the Arecaceae plants for enhanced wastewater treatment

Arecaceae presents one of the plant families distributed mainly in the equatorial and subequatorial regions. Arecaceae are widely applied in many fields such as food, cosmetics, fuel, and chemical industries. However, a large amount of agricultural waste from the Arecaceae trees has been released into the environment. The objective of this report is to gain more insights into the potentials and applications of activated carbon (AC) from the Arecaceae trees in wastewater treatment, in which, the ability to handle organic pigments, metals, and antibiotics is focused. The physical properties and processability of AC are statistically evaluated. With a uniform structure, large specific surface area, processing ability according to Langmuir and pseudo-second-order models, we showed that ACs from Arecaceae trees are promising materials for water treatment applications. This is the basis for the development and reduction of by-products that affect the environment.

The sorption of Tebuconazole and Linuron from an Aqueous Environment with a Modified Sludge-Based Biochar: Effect, Mechanisms, and Its Persistent Free Radicals Study

In this study, the sludge-based biochar was prepared and utilized as an adsorbent for the removal of two commonly used pesticides in agriculture, namely tebuconazole (Teb) and linuron (Lin) in an aqueous solution. The main contributing factors such as biochar preparation conditions, persistent free radicals as well as contact time, agitation speed, biochar dose, temperature, and pH were investigated. The physicochemical properties were characterized by SEM + EDS, FTIR, BET, EPR, etc. The results showed that the maximum adsorption capacities based on the Langmuir model was 7.8650 mg g−1 for tebuconazole and that based on Freundlich model was 9.0645 mg·g-1 for linuron at 25°C. The pseudo-second-order kinetic equations were all fitted well to the kinetic process of the adsorption of the two pesticides with all R2 ≥ 0.915. The maximum values of tebuconazole adsorption capacity occur at pH = 3. Meanwhile, linuron was not affected by pH. Both Cr6+ (r = −0.793∗∗/ −0.943∗∗) and humic acid (r = −0.798∗∗/ −0.947∗∗) significantly inhibited the adsorption amount of tebuconazole and linuron onto the biochar. Electron spin resonance signals (ESR) indicated that environmentally persistent radicals (EPFRs) are preferentially formed at lower pyrolysis temperatures and lower transition metal concentrations. The g-factors for BC400, BC600, BCF400, and BCF600 were 2.0036, 2.0035, 2.0034, and 2.0033, respectively, indicating that the EPFRs mainly have a carbon-centered structure with adjacent oxygen atoms. In addition, to close to the actual situation, natural water (from YanTai) was collected to simulate pesticide contamination. This study demonstrates that sludge-based biochar can achieve efficient removal of tebuconazole and linuron in aqueous environment in a short period of time with no secondary environmental risk especially on the waste activated sludge.

Designing chitosan based magnetic beads with conocarpus waste-derived biochar for efficient sulfathiazole removal from contaminated water

The development of a simple method to synthesize highly efficient and stable magnetic microsphere beads for sulfathiazole (STZ) removal from contaminated aqueous media was demonstrated in this study. Conocarpus (Conocarpus erectus L.) tree waste (CW) derived biochar (BC) was modified to fabricate chitosan-BC (CBC) and magnetic CBC (CBC-Fe) microsphere beads. Proximate, chemical, and structural properties of the produced adsorbents were investigated. Kinetics, equilibrium, and pH adsorption batch trials were conducted to evaluate the effectiveness of the synthesized adsorbents for STZ removal. All adsorbents exhibited the highest STZ adsorption at pH 5.0. STZ adsorption kinetics data was best emulated using pseudo-second order and Elovich models. The equilibrium adsorption data was best emulated using Langmuir, Freundlich, Redlich-Peterson, and Temkin models. CBC-Fe demonstrated the highest Elovich, pseudo-second order, and power function rate constants, as well as the highest apparent diffusion rate constant. Additionally, Langmuir isotherm predicted maximum adsorption capacity was the highest for CBC-Fe (98.67 mg g-1), followed by CBC (56.54 mg g-1) and BC (48.63 mg g-1). CBC-Fe and CBC removed 74.5%-108.8% and 16.2%-25.6% more STZ, respectively, than that of pristine BC. π-π electron-donor-acceptor interactions and Lewis acid-base reactions were the main mechanisms for STZ removal; however, intraparticle diffusion and H-bonding further contributed in the adsorption process. The higher efficiency of CBC-Fe for STZ adsorption could be due to its magnetic properties as well as stronger and conducting microsphere beads, which degraded the STZ molecules through generation of HO• radicals.

Advances in decontamination of wastewater using biomass-basedcomposites: A critical review

Contaminant removal from wastewater using natural biosorbents has been widely studied as a suitable and environmentally benign alternative for conventional techniques. Currently, researchers are working on various biomass-based composites for wastewater remediation to improve the performance of natural biosorbents. This review takes into focus a wide range of biomass-based composites like hydrogel composites, metal oxide composites, magnetic composites, polymer composites, carbon nanotubes (CNTs) and graphene composites, metal organic framework composites (MOFs) and clay composites for the removal of various contaminants from wastewater. It is evident from the literature survey that the composite fabrication involves the modification of morphological and textural features of the biomass which results in significant enhancement of adsorption capacity. Apart from this, regeneration of the used biomass-based composite is also studied in depth in order to overcome the problem of solid waste generation. This review would prove to be beneficial for researchers who are currently focusing on the development of cost-effective, easily available, recyclable biomass-based composites with enhanced adsorption capacities for wastewater treatment.

Re-recognizing micro locations of nanoscale zero-valent iron in biochar using C-TEM technique

Biochar supported nanoscale zero-valent iron (NZVI/BC), prepared commonly by liquid reduction using sodium borohydride (NaBH₄), exhibits better reduction performance for contaminants than bare NZVI. The better reducing ability was attributed to attachment of nanoscale zero-valent iron (NZVI) on biochar (BC) surface or into the interior pores of BC particles due to observations by scanning electron microscopy (SEM) and plan transmission electron microscopy (P-TEM) techniques in previous studies. In this study, cross-sectional TEM (C-TEM) technique was employed firstly to explore location of NZVI in NZVI/BC. It was observed that NZVI is isolated from BC particles, but not located on the surface or in the interior pores of BC particles. This observation was also supported by negligible adsorption and precipitation of Fe²⁺/Fe³⁺ and iron hydroxides on BC surface or into interior pores of BC particles respectively. Precipitation of Fe²⁺ and Fe³⁺, rather than adsorption, is responsible for the removal of Fe²⁺ and Fe³⁺ by BC. Moreover, precipitates of iron hydroxides cannot be reduced to NZVI by NaBH₄. In addition to SEM or P-TEM, therefore, C-TEM is a potential technique to characterize the interior morphology of NZVI/BC for better understanding the improved reduction performance of contaminants by NZVI/BC than bare NZVI.