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ABSTRACT This work presents a scalable, bottom‐up approach for doping quantum confined, 1D lepidocrocite (1DL) titanate nanofilaments (NFs) with transition metal (TM) cations Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, and Cu²⁺ to enhance their photo‐ and electrocatalytic properties. Here we react titanium oxysulfate with tetramethylammonium hydroxide at 80°C for 12 h at one atmosphere. By incorporating metal salts during synthesis, uniform doping within the 1DL backbone is achieved. The resulting TM‐doped 1DL NFs all exhibit lower bandgap energies, E_g, than the undoped samples (3.89 eV); some by as much as 0.8 eV for Mn²⁺ at 1 mol% doping, extending optical absorption into the visible region. X‐ray diffraction, scanning electron microscopy, UV–Vis spectroscopy, inductively coupled plasma analysis, and X‐ray photoelectron spectroscopy confirm the successful doping and structural integrity of our materials. The photocatalytic performance of the 1 mol% doped NFs is significantly enhanced, with a 95% degradation of rhodamine 6G dye under visible light in just 30 min, compared to only 65% degradation for the undoped 1DL NFs. In electrocatalysis, the Ni‐doped 1DL NFs show superior oxygen evolution reaction (OER) activity, with an overpotential of 319 mV at 10 mA cm⁻², which is lower than the 383 mV for undoped 1DL NFs. The Ni‐doped 1DL also has the lowest Tafel slope of 145 mV/dec at 1 mol% doping and 143 mV/dec at 5 mol%, compared to 204 mV/dec for the undoped 1DLs, indicating faster reaction kinetics. The Ni‐doped NFs also exhibit excellent stability, maintaining a constant potential at 10 mA cm⁻²for > 50 h. Adding methanol to all colloidal suspensions results in their gelation within seconds. These findings highlight the potential of TM doping as an effective strategy to optimize 1DL's electronic and photochemical catalytic properties. 

ABSTRACT Herein we report on the facile, one‐pot, scalable, room‐temperature (RT) synthesis of quantum‐confined, 1D lepidocrocite (1DL) titanate nanofilaments (NFs)—by reacting titanium oxysulfate with tetramethylammonium hydroxide, both cheap and ubiquitous precursors—for times that are significantly shorter than previously reported synthesis methods that required 80°C and, in some cases, days of reaction time. Samples are characterized by X‐ray diffraction, Raman and X‐ray photoelectron spectroscopies, small angle X‐ray scattering, SAXS, scanning and transmission electron microscopy, revealing no significant differences from the higher‐temperature synthesis methods, except in the fact that the lengths of the NFs varied. A parallelepiped model, one lepidocrocite layer thick, is used to fit the SAXS patterns of colloidal suspensions, CSs. The ribbons made from material reacted for 4 h are ≈33 nm long and 2.7 nm wide; after 12 h reaction time their lengths are >100 nm and their widths are ≈3.0 nm. This is the first diffraction‐based evidence that the ribbons actually lengthen with time. Powders made using this method can be dried and re‐dispersed in water. The resulting CS adsorbed more rhodamine 6G than any previous 1DL‐based CS tested. From Tauc plots, we obtain bandgap energies of ≈4.0 eV, which is only weakly dependent on reaction time. This work establishes a simple, one‐pot, RT, atmospheric‐pressure, inexpensive and highly scalable method to synthesize quantum‐confined titanate‐based nanomaterials optimized for photocatalytic, environmental, and optoelectronic applications among others.