A series of black TiO₂ with and without the addition of urea were successfully prepared using a simple one-step synthetic method by calcination under different atmospheres (vacuum, He, or N₂). The physicochemical, optical, and light-induced charge transfer properties of the as-prepared samples were characterized by various techniques. It was found that a vacuum atmosphere was more beneficial for the formation of oxygen vacancies (OVs) than the inert gases (He and N₂) and the addition of urea-inhibited OVs formation. The samples annealed in the vacuum condition exhibited better visible-light adsorption abilities, narrower bandgaps, higher photo-induced charge separation efficiency, and lower recombination rates. Hydroxyl radicals (·OH) were the dominant oxidative species in the samples annealed under a vacuum. Finally, the samples annealed under vacuum conditions displayed higher photocatalytic activity for methylene blue (MB) degradation than the samples annealed under He or N₂. Based on the above, this study provides new insights into the effects of annealing atmospheres and urea addition on the properties of black TiO₂.

Black TiO₂ with doped nitrogen and modified carbon (b-N-TiO₂/C) were successfully prepared by sol-gel method in the presence of urea as a source of nitrogen and carbon. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, electron paramagnetic resonance (EPR), and UV-vis diffuse reflectance spectra (DRS). The doped nitrogen, introduced defects, and modified carbon played a synergistic role in enhancing photocatalytic activity of b-N-TiO₂/C for the degradation of chlorophyll-a in algae cells. The sample, with a proper amount of phase composition and oxygen vacancies, showed the highest efficiency to degrade chlorophyll-a, and the addition of H₂O₂ promoted this photocatalysis degradation. Based on the trapping experiments and electron spin resonance (ESR) signals, a photocatalytic mechanism of b-N-TiO₂/C was proposed. In the photocatalytic degradation of chlorophyll-a, the major reactive species were identified as OH and O₂⁻. This research may provide new insights into the photocatalytic inactivation of algae cells by composite photocatalysts.

This research evaluated the efficacy of using two types of biochar (non-modified and acidified) from date palm residues (fronds, leaves, pits) as soil amendments for enhancing soil fertility and maize growth. These biochars were produced through slow pyrolysis under oxygen-limited conditions at 500 °C. Our innovative approach was to minimize gas emissions by converting smoke into liquid fertilizer (LS), which was expected to improve seed germination and early plant growth stages. To assess this aim, a completely randomized experiment was conducted under lab conditions, in which 10 maize seeds were placed on double filter papers in Petri dishes and then exposed to seven concentrations of LS (0.0, 0.01, 0.10, 1.0, 10 and 100%, using distilled water for dilution v/v). The LS contains nutrients and bioactive compounds that may enhance seed germination and early plant growth at low concentrations, whereas higher concentrations may cause phytotoxic effects. Results showed that liquefied smoke at 0.1% increased the absolute percentage of maize germination from 75% (control) to 100% and achieved the highest root length of 9.80 cm. Acidified biochars at 5% reduced soil pH from 8.87 to 8.12 and enhanced potassium availability to 87.93 mg kg⁻¹. Conversely, the non-modified biochars contributed to further increases in soil organic matter (up to 1.02%), nitrogen, and phosphorus. In addition, the application of acidified leaf biochar (5%) enhanced maize shoot growth by 133%, chlorophyll content by 39%, and potassium uptake by 110%. This research establishes a scalable approach for converting agricultural waste into climate-resilient resources, effectively addressing soil degradation in arid environments, boosting crop resilience, and furthering the objectives of a circular bioeconomy.

The limited nitrogen and phosphorus concentration reduction performance of wetlands during cold weather is a global concern. To address the challenge of low nutrient removal efficiency in winter, this study introduces a hollow fiber membrane module integrated into paddy soil, enabling the in situ formation of a hydrogen-based bacterial–algal biofilm. Over a 60-day experiment at water temperatures of 6.2–15.0 °C, the biofilm-enhanced system (HS) reduced aqueous ${\mathrm{NH}}_4^{+}$-N from 25 mg/L to 0.2 mg/L by day 30 and maintained this low level through day 60, whereas the S system still had 5.5 mg/L ${\mathrm{NH}}_4^{+}$-N. Moreover, the HS system consistently maintained lower ${\mathrm{NO}}_3^{-}$-N and total phosphorus (TP) concentrations than the S system. Microbial communities were characterized using third-generation 16S full-length sequencing and 18S rRNA V4 amplicon sequencing. The biofilm was dominated by Geminocystis_PCC_6308, Rikenellaceae_RC9_gut_group, and Rhodobacter, while eukaryotic green algae, mainly Botryococcus sp., were also abundant. In the paddy soil, Terrimonas and unclassified_AKYH767 were identified as potential key taxa associated with nitrogen and phosphorus concentration reduction. Overall, the hydrogen-based bacterial–algal biofilm effectively improves the nitrogen and phosphorus concentration reduction of paddy soil wetlands, offering a promising strategy for cold-weather eutrophic water remediation.

Excessive N and P discharges into aquatic environments contribute to water pollution and eutrophication. Thus, there is an urgent need for low-cost and sustainable adsorbents for contaminant removal. In this study, biochar was prepared from date palm fronds, leaves, and pits through slow pyrolysis followed by MgFe-LDH modification at a Mg/Fe molar ratio of 3:1. The FTIR results demonstrate that the MgFe-LDH modification added more hydroxyl groups, interlayer carbonate species, and metal–oxygen bonds. The removal efficiency of the investigated nutrients increased considerably with increasing sorbent dosage, with MgFe-LDH modification being most effective. Generally, sorption followed typical hyperbolic adsorption patterns, approaching equilibrium after 120–180 min. Both Langmuir and Freundlich isotherms adequately described nutrient sorption on unmodified biochars, while the Freundlich model provided a better fit on MgFe-LDH. LDH/BC derived from pits exhibited excellent adsorption capacities, i.e., 105 mg/g for NO3-, 103 mg/g for NH₄⁺, and 135 mg/g for PO₄³⁻. Pseudo-second-order kinetics best described NH₄⁺ adsorption, while both pseudo-first-order and pseudo-second-order models were well fitted to NO₃⁻ and PO₄³⁻ adsorption. Overall, MgFe-LDH modification offers a promising engineering strategy for converting date palm residues into multifunctional adsorbents and offers insight into the design of waste-derived materials for nutrient recovery and eutrophication control.