ZnO nanoparticles (NPs) were prepared by green synthesis using plant leaf extraction of Ochradenus baccatus and characterized by XRD, FESEM, HRTEM, and Raman spectroscopy techniques. Since elevated CO levels have been associated with inflammatory conditions, cardiovascular diseases, and respiratory disorders and the methane gas primarily produced by gut microbiota and linked to gastrointestinal disorders and other abnormal methane levels in breath samples, the nanoparticles were applied for gas sensor fabrication. Thus, the gas sensors fabricated using ZnO nanoparticles were investigated for CH4 , H2 , CO, and NO2 gases. The gas sensing was performed for the fabricated sensors at various operating temperatures and gas concentrations. Interestingly, leaf-extracted green synthesized ZnO NPs were more sensitive to CH4 , CO, and NO2 gases than to H2 . The results of sensing studies revealed that the nanoparticles exhibit a selectivity toward gas depending on the gas type. The sensor response was also studied against the humidity. These findings bridge between the laboratory and industry sectors for future gas sensors development, which can be used for exhaled breath analysis and serve as potential diagnostic tools for highly sensitive contagious diseases.

Water pollution is one of the main challenges currently facing scientists around the world because of the rapid growth in industrial activities. On this basis, 2D nanolayered and nanohybrid structures, which are based on a ternary system of nickel–titanium–zinc, are considered favorable sources for designing effective nanocomposites for the photocatalytic degradation of industrial pollutants in a short period of time. These nanocomposites were designed by modifying twodimensional nanolayers to produce a three-dimensional porous structure of multi-doped Ni/Ti-ZnO nanocomposites. Additionally, another additive was produced by constructing nanohybrids of nickel– titanium–zinc combined with a series of hydrocarbons (n-capric acid, myristic acid, stearic acid, suberic acid, and sebacic acid). Energy-dispersive X-ray spectrometry, X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermal analyses confirmed the growth of the nanolayered and nanohybrid materials in addition to the production of nanocomposites. The positive role of the dopants (nickel and titanium) in producing an effective photocatalyst was observed through a significant narrowing of the band gap of zinc oxide to 3.05–3.10 eV. Additionally, the high photocatalytic activity of this nanocomposite enabled the complete removal of colored dye from water after 25 min of UV radiation. In conclusion, this study proposes an unconventional approach for designing new optical nanocomposites for purifying water. Additionally, it suggests a novel supporting method for designing new kinds of nanohybrids based on multi-metals and organic acids.

We report an economical approach for the fabrication of laser-produced graphene (LPG) electrodes, which results in an improved electrochemical performance. Polyimide polymer was used as the starting material for LPG synthesis and was irradiated under ambient conditions with a CO2 laser. The prepared LPG samples were characterized by Raman spectroscopy and FTIR, which validated the formation of multilayer graphene containing sp2 hybridized C＝C bonds. FE-SEM revealed three-dimensional (3D) sheet-like structures, while HR-TEM images showed lattice planes with an interplanar spacing of approximately 0.33 nm, corresponding to the (002) plane of graphene. Their electrochemical performance showed a remarkable areal specific capacitance (CA) of 51 mF cm−2 (170 F g−1) at 1 mA cm−2 (3.3 A g−1) in a three-electrode configuration with 1 mol L−1 KOH as the aqueous electrolyte. The LPG electrodes produced an energy density of ~3.5 µWh cm−2 and a power density of ~350 µW cm−2, demonstrating significant energy storage ability. They also had an excellent cycling stability, retaining 87% of their specific capacitance after 3 000 cycles at 1 mA/cm2. A symmetric supercapacitor fabricated with LPG electrodes and the 1 mol L−1 KOH electrolyte had a specific capacitance of 23 mF cm−2 and showed excellent retention after 10 000 cycles, showing LPG’s potential for use in supercapacitors. Key words: Supercapacitors; Graphene; LPG; Electrochemical studies; Charge storage mechanism

This study reports the use of tin oxide (SnO2) octahedral nanoparticles with exposed high-energy facets as sensing material in inkjet-printed carbon monoxide (CO) gas sensors. The nanoparticles were synthesized via a hydrothermal method aimed at encouraging high-indexed (221) crystal planes to be exposed as facets, since their high surface energy may encourage interactions with gases. Studies by X-ray diffraction (XRD) confirmed the identity of the SnO2, while transmission electron microscopy (TEM) revealed formations of octahedral-shaped SnO2 nanoparticles, with features confirming the exposure of high-energy (221) crystal facets. The nanoparticles’ reductive behavior in a CO environment was studied using temperature-programmed reduction (TPR). A stable ink based on the SnO2 nanoparticles was successfully prepared and utilized to fabricate, via inkjet printing, homogenous films onto electrically conductive graphene-based interdigitated electrodes. Optimizing the inkjet printing parameters enhanced the CO gas sensing performance of the fabricated sensors. For example, at 200 ppm, the sensor with 10 printed layers recorded a sensitivity of about 20%, as compared to a sensitivity of not more than 14% recorded in each of the sensors with 5, 15, and 20 printed layers. As a result of having homogenous films, the inkjet-printed sensors also exhibited almost double the sensitivity of similar sensors prepared by drop-casting method.

Tannery wastewater is a major environmental pollutant that introduces toxic compounds, including chromium (Cr), into agricultural soils, posing significant challenges to plant growth and productivity. This research uniquely evaluates the efficacy of three specific plant growth-promoting rhizobacteria (PGPR)—Paenibacillus polymyxa, Bacillus amyloliquefaciens, and Pseudomonas putida—for mitigating Cr stress in rice (Oryza sativa L.). In this study, O. sativa plants were exposed to different levels of tannery wastewater (0%, 50%, and 100%) in a controlled pot experiment to assess the impact of P. polymyxa, B. amyloliquefaciens and P. putida on various morpho-physio-biochemical traits. Results from the present study revealed that the Cr toxicity induced a substantial decrease in shoot length, root length, number of leaves, leaf area, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), and phosphorus (P) contents in the plants. However, Cr stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), which also led to an increase in various enzymatic and nonenzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant (P < 0.05) increase in proline metabolism, the AsA–GSH cycle, and the pigmentation of cellular components was observed. Addition of P. polymyxa, B. amyloliquefaciens and P. putide into the soil significantly alleviated Cr toxicity effects on O. sativa by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in organic acid and PGPRs-treated plants seem to play a role in capturing stress-induced reactive oxygen species as was evident from lower levels of MDA and H₂O₂. Moreover, the application of different PGPRs enhanced both the abundance and diversity of the rhizosphere microbiome, with bacterial population levels and Shannon diversity indices significantly increasing. A marked reduction in daily Cr intake and associated health risks was also observed under these treatments, and proteomic responses under Cr stress. Research findings, therefore, suggested that the application of PGPRs can ameliorate Cr toxicity in O. sativa seedlings and resulted in improved plant growth and composition under metal stress.

Soil contamination with toxic heavy metals such as aluminum (Al) is becoming a serious global problem due to the rapid development of the social economy. Organic acid and earthworms (Eisenia fetida) are efficient, environmentally friendly, and biodegradable and they enhance the solubility, absorption, and stability of metals. Therefore, the present study was conducted to investigate the individual and combined effects of organic chelating agents such as ascorbic acid and malic acid (5.0 µM L⁻¹ each) and earthworms (Eisenia fetida, 10 individuals per pot) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), ASA–GSH cycle, cellular fractionation, and their specific gene expression, sugars, nutritional status of the plant, Al accumulation from the different parts of the plants, Al uptake, rhizosphere microbiome, health risk, and proteomic responses, in rice (Oryza sativa L. cv. IR-64) grown in soil spiked with Al [100 mg kg⁻¹ ]. Results from the present study revealed that the Al toxicity induced a substantial decrease in shoot length, root length, number of leaves, leaf area, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca^2 +)^, magnesium (Mg²⁺), iron ( Fe²⁺), and phosphorus (P) contents in the plants. However, Al stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), which also led to an increase in various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant (P < 0.05) increase in proline metabolism, the AsA–GSH cycle, and the pigmentation of cellular components was observed. Addition of organic acid and E. fetida into the soil significantly alleviated Al toxicity effects on O. sativa by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in organic acid and E. fetida-treated plants seem to play a role in capturing stress-induced reactive oxygen species as was evident from lower levels of MDA and H₂O₂. Moreover, the application of organic acids and E. fetida enhanced both the abundance and diversity of the rhizosphere microbiome, with bacterial population levels and Shannon diversity indices significantly increasing. A marked reduction in daily Al intake and associated health risks was also observed under these treatments, and proteomic responses showed downregulation of HSP70, MT2A, and PRP under Al stress. Research findings, therefore, suggested that individual and combined application of organic acid and E. fetida can ameliorate Al toxicity in O. sativa seedlings and resulted in improved plant growth and composition under metal stress.

Study region

This study focuses on an arid zone of Saudi Arabia that is experiencing rapid urban growth and escalating water scarcity. The region encompasses major cities such as Mecca, Jeddah, Khulays, and Rabigh, where the demand for sustainable water resource management is becoming increasingly urgent due to the limited availability of natural freshwater sources. The challenge is further intensified by ongoing urbanization and large-scale economic developments, particularly around Mecca, Jeddah, King Abdullah Economic City, and Yanbu Industrial City, which place additional pressure on the region’s fragile water systems.

Study focus

The objective of this research is to assess and map the suitability of rainwater harvesting (RWH) sites using an integrated approach that combines Geographic Information System (GIS), the Analytic Hierarchy Process (AHP), and Multi-Criteria Decision Analysis (MCDA). The analysis incorporates hydrological, geological, and infrastructural criteria, guided by Food and Agriculture Organization (FAO) guidelines. The study also evaluates the performance and contribution of existing RWH infrastructure and identifies optimal locations for future dam construction.

New hydrological insights for the region

The results indicate that approximately 6000 km² (∼26 % of the study area) is highly suitable for RWH, with an estimated surface runoff potential of about 730 million m³ . Existing dams—Khlays, Rabiigh, and Fatima—play a significant role in regional water supply. Four primary locations—Ghoran, Thule, Qahah, and Fatima—were identified as optimal for new dam sites, with estimated water storage capacities calculated. These findings demonstrate the potential of integrated RWH planning to enhance renewable water resources, support long-term water security, and inform policy and infrastructure development in arid regions like Western Saudi Arabia.