We present first-principles density-functional calculations for the structural, electronic and magnetic properties of monolayer graphene doped with 3d (Ti, V, Cr, Fe, Co, Mn and Ni) metal trioxide TMO3 halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO3 halogen cluster was embedded in monolayer graphene substituting four carbon (C) atoms (ii) three C atoms were substituted by three oxygen (O) atoms in one graphene ring and TM atom was adsorbed at the hollow site of O atoms substituted graphene ring. All the impurities were tightly bonded in the graphene ring. In first case of TMO3 doped graphene layer, the bond length between C-O atom was reduced and bond length between C-O atom was increased. In case of Cr, Fe, Co and Ni atoms substitution in between the O atoms, leads to Fermi level shifting to conduction band thereby causing the Dirac cone to move into valence band, however a band gap appears at high symmetric K-point. In case of TiO3 and VO3 substitution, system exhibits semiconductor properties. Interestingly, TiO3-substituted system shows dilute magnetic semiconductor behavior with 2.00 mu B magnetic moment. On the other hand, the substitution of CoO3, CrO3, FeO3 and MnO3 induced 1.015 mu B, 2.347 Its, 2.084 mu B and 3.584 mu B magnetic moment, respectively. In second case of O atoms doped in graphene and TM atoms adsorbed at the hollow site, the O atom bulges out of graphene plane and bond length between TM-O atom is increased. After TM atoms adsorption at the O substituted graphene ring the Fermi level (E-F) shifts into conduction band. In case of Cr and Ni adsorption, system displays indirect band gap semiconductor properties with 0.0 mu B magnetic moment. Co adsorption exhibits dilute magnetic semiconductor behavior producing 0.916 mu B magnetic moment. Fe, Mn,Ti and V adsorption introduces band gap at high symmetric K-point also inducing 1.54 mu B, 0.9909 mu B, 1.912 mu B, and 0.98 mu B magnetic moments, respectively. Our results show that 3d metal trioxide TMO3 halogen substituted monolayer graphene has potential applications in nanoelectronics, spintronics and magnetic storage devices. (C) 2016 Elsevier B.V. All rights reserved.