We report a high-throughput method of generating graphene monolayer (>90% yield) from weakly oxidized, poorly dispersed graphite oxide (GO) aggregates. These large-sized GO aggregates consist of multilayer graphite flakes which are oxidized on the outer layers, while the inner layers consist of pristine or mildly oxidized graphene sheets. Intercalation-exfoliation of these GO aggregates by tetrabutylammonium cations yields large-sized conductive graphene sheets (mean sheet area of 330 +/- 10 microm(2)) with high monolayer yield. Thin-film field-effect transistors made from these graphene sheets exhibit high mobility upon nullifying Coulomb scattering by ionic screening. Ionic screening versus chemical doping effects of different ions such as chloride and fluoride on these graphene films were investigated with a combination of in situ Raman spectroscopy and transport measurement.